Environmental Pollution

Happy Diwali (Deepavali)!

No doubt Diwali will be celebrated across the world, as are many important events on the calendar, through the setting off of lots of fireworks. The spectacles produced are brilliant, of course ~ but they are costly, and not only in terms of the cost of the fireworks and the impacts on our pets. Fireworks are also highly polluting and have the potential to impact negatively environmental quality and our health.

Aside from the littering caused by all those spent fireworks – no surprises there, what goes up has to come down – ever wondered what all those bright colours are formed from? They are formed from the high temperature combustion of compounds containing heavy metals (“heavy metal salts”). Sparkling green colours are produced by barium chloride, blue is produced by copper chloride. Strontium carbonate is used to produce red fireworks, calcium chloride ~ orange fireworks, sodium nitrate ~ yellow fireworks. Purple fireworks are typically produced by use of a mixture of strontium (red) and copper (blue) compounds. The list goes on and on ….

Combustion also yields other pollutants, notably fine particulate matter (including PM10 and PM2.5, but no doubt even finer particles too), sulfur dioxide (SO2), persistent organic pollutants (PoP) polycyclic aromatic hydrocarbons (PAHs) and highly toxic dioxins. None of these are good for us. And that is not all, of course we have developed fireworks that make louder bangs and travel to higher altitudes in the sky. This is all based on chemistry and chemical reactions, but also involves some very old technology – gunpowder, which is believed to have been invented in China over 1000 years ago! Thus as Licudine et al. (2012) reported in the journal Public Health Reports, based on their study of air pollution linked to new year firework celebrations on Hawaii (see paper linked below), “chlorates or perchlorates can be used to achieve noise levels equivalent to trinitrotoluene and result in more violent explosions than traditional nitrates … Lead (Pb) salts are widely used as igniters to initiate fireworks explosions. Manganese (Mn) and Mn dioxide serve as fuel and oxidizer for brighter lights, chromium (Cr) is used as a burn rate catalyst for propellants,and nickel (Ni) acts as an electric firing device for fireworks.” The health effects of heavy metals are well-known, and many of the emissions from fireworks persist in the environment long after the spectacle of the display is over. The authors go on to state that “perchlorates have been associated with thyroid problems, and toxic byproducts (e.g., dioxins) could be produced as a result of atmospheric reactions between metal oxides and organic fuels.”

Licudine et al. (2012) is not the only study on fireworks as a source of environmental pollution. In fact there have been many such studies. One of these investigated air quality in Delhi, India, during the Diwali celebrations. Delhi is already one of the world’s most polluted cities, particularly during the Northern Hemisphere autumn and winter months (which is when Diwali takes place) when local weather conditions and the burning of fossil fuels and biomass for heat, transport and cooking conspire to produce some of the poorest air qualities ever recorded globally. The study by Peshin et al (2017 – and see link below to the paper) recorded substantial increases in SO2, nitrogen dioxide (NO2) – a greenhouse gas and cause of environmental acidification, ozone (O3), fine particulate matter (including black carbon, or soot) and trace metals during firework displays associated with Diwali celebrations.

Similar findings have also been reported for Jamshedpur in the east Indian state of Jharkhand, suggesting that firework-related pollution is a widespread problem in India during Diwali celebrations (Ambade, B. The air pollution during Diwali festival by the burning of fireworks in Jamshedpur city, India. Urban Climate 26, 149-160). The setting-off of firecrackers is highlighted in this article as a particularly rich source of pollution, as it is here (for Delhi) and here (for China).

An even more recently published article – just out in the Journal of Cleaner Production, emphasises that “[r]ecreational fireworks use causes some of the most extreme urban particulate matter pollution: Hourly peaks over 1000 ug/m3 PM10 have been measured during the Chinese New Year and Indian Diwali festivals …. [f]ireworks plumes can be detected over a long range, between regions and countries, in the form of elevated particulate matter (PM10 and PM2.5) and water-soluble potassium … [i]n Western Europe, fireworks celebrations have contributed to significant annual atmospheric metal emissions, to the urban background of trace metals, and to a localized perchlorate pollution in surface and groundwater” (Andradottir and Thorsteinsson, 2019). Unfortunately this article is not available for public download, but it is accessible via NUS’s excellent library in digital form: Andradottir, H.O. and Thorsteinsson, T. (2019) Repeated extreme particulate matter episodes due to fireworks in Iceland and stakeholders’ response. Journal of Cleaner Production, 236, 11711.

One of the points raised by Andradottir and Thorsteinsson (2019) is the “passiveness” of the general public when it comes to the pollution and health risks of firework displays. The authors of the paper claim that this in part stems from a lack of awareness of the link to pollution. The authors argue that the general public should be made more aware and that the purchasing of less environmentally damaging fireworks should be encouraged (for example, Disney uses fireworks that are propelled by compressed air rather than gunpowder – why cannot others follow suit?).

We need also to be mindful of the costs of producing and transporting fireworks to their point of use, and the risks posed to those involved in their manufacture. An estimated 90% of the world’s fireworks are manufactured in China – often in rural areas, with women predominantly involved in actually making the fireworks, handling dangerous chemicals with little formal training. Accidents happen, often with lethal consequences – as is evident from the webpage linked here. Accidents are also commonplace in Sivakasi, the city in Tamil Nadu that is commonly regarded as India’s “fireworks capital“. Whoever thinks about the conditions fireworks are produced under, and what health-threatening substances and practices those involved in the manufacture of fireworks are exposed to, when purchasing fireworks or going along to a display? Do we really think that those toxic substances used in manufacturing never leak out into the environment even before the fireworks are used? And what about all that packaging that comes with fireworks – where does that all end up?

It could be argued that what we are actually celebrating through our firework displays is our reckless disregard for our environment, for the economically marginalised and, ultimately, for ourselves.

By now Environmental Pollution students at NUS are probably either bored or confused by my seemingly constant references to pH, acid deposition, acidification and their role in environmental pollution and its effects. The truth is, pH, and more particularly variations in pH, has a major part to play in discussions concerning environmental pollution; changes in pH can be an effect (a result) of pollution. Moreover, pH variations can influence the amount of human and ecosystem harm caused by other chemicals in the environment, such as heavy metals, but also impact the availability of nutrients essential to the fertility of soil and hence to plant growth and crop productivity. Already in GE3246 we have discussed acid deposition – its sources and effects. A major source is air pollution in the form of carbon, sulfur and nitrogen oxides [CO₂, SO₂ & NO] released from power stations etc. Ammonia (‎NH₃), associated with traffic pollution and the misuse of fertliizer, is also a source of acidification pressure. These gases combine with moisture in the atmosphere to form acid and when deposited go on to cause acidification of lakes and rivers and the ocean. In the lecture this coming week we will add the acidification of soils and its effects to this list ….

Environmental acidification occurs naturally, of course, particularly where the underlying geology is base-poor. Humans have through their activities made the situation far worse, however, by causing anthropogenic (or cultural) acidification.

So what is pH and how is it linked to environmental acidification and anthropogenic acidification in particular?

The Danish scientist S. P .L. Sørensen first introduced the term pH (though he denoted it as p_H) to mean the amount (or power) of hydrogen (H⁺) ions (protons) in a solution. If a solution (e.g. lake or ocean water, or even the water between individual particles of soil, known as soil pore water) becomes more or less acidic, the concentration of H⁺ ions becomes stronger or weaker. Acidity (or its converse alkalinity) is the amount of hydrogen and hydroxide (OH^–) ions present in solution, or relative concentrations of these. As acidity increases, the amount of H⁺ ions increases while levels of OH^– ions decline. The table below shows the reciprocal relationship between H⁺  and OH^– ions.

Note that the pH scale ranges from 0 to 14.  Solutions with a pH less than 7 are generally referred to as acidic, while those with a pH greater than 7 are basic or alkaline. A pH of 7.0 is taken to be neutral, because the H⁺ and OH^– ions balance one another. It is perhaps worth pointing out that temperature directly effects pH. An increase in temperature causes ionisation to proceed at a higher rate than at lower temperature, causing more H ions to be freed from water molecules ( H2O ⇌ 2H⁺ + OH^– ). It is also worth pointing out that pH is the negative log of the molar hydrogen ion concentration (-log₁₀[H⁺], or [H⁺] = 10^-pH). What that means in English is that as pH falls, acidity increases, and a pH fall of 1.0 unit represents a 10x increase in acidity (or 10 x more H⁺ ions)!

So how is pH linked to anthropogenic acidification and its environmental effects, such as coral and forest death?

Hydrogen ions are highly positively charged (the ⁺ indicates that). Hence acids can be highly reactive and corrosive (ever spilt battery acid on your clothes?). OH^– is also highly reactive, hence strong alkaline solutions, such as bleach, are highly caustic (common bleach is Sodium hypochlorite, NaClO, composed of one sodium (Na) atom, one chlorine (Cl) atom and one oxygen (O) atom.). Heavy metals are also positively charged (positively charged atoms are known as cations – e.g. copper (Cu²⁺), magnesium (Mg²⁺), manganese (Mn²⁺),  lead (Pb²⁺), zinc (Zn²⁺)), in fact most inorganic contaminants are positively charged (or cations). Many nutrients that plants required (e.g. Potassium, K⁺, Calcium, Ca²⁺) are also cations. This sounds confusing, but some metals, including some heavy metals (copper, iron, zinc etc), are classed as nutrients at low concentrations (i.e. they are micro-nutrients) but are toxic at higher concentrations. As mentioned in an earlier lecture, the dose makes the poison (although hopefully everyone realises by now that this is a gross over-simplification).

Acidification has direct effects on biota. Generally however its effects are less direct, and take place through the effects on concentrations of heavy metals, water transparency, availability of nutrients, including calcium carbonate (CaCO3), the material for coral exoskeletons. The infografic below shows how key aquatic organisms may be lost as the pH of their habitat becomes more acidic.

Acidification impacts soils through changing the availability of chemical elements, some of which can be harmful to biota and have negative impacts on agricultural productivity. Soil particles, organic matter etc, tend to be negatively charged – and therefore they can hold (adsorb) cations on their surface (when something is adsorbed on a surface it is basically adhered, or stuck/glued, to the surface). Soils differ in this ability – known as Cation Exchange Capacity (CEC), depending on their texture (e.g. proportion of clay, silt and sand sized particles, amount of organic matter). Generally  organic-rich, finely textured soils have have high CEC – they are sticky as far as nutrients and other cations go – and are therefore often relatively “fertile”, and good for agriculture. Coarse-grained (with a high proportion of sand-sized particles) soils with low organic matter content tend to have low CEC, and any nutrients present may be easily lost to leaching and flooding of the soil. The schema below shows how the finest plant roots (root hairs) interact with surrounding soil particles and soil pore water, and the cations attached to negatively-charged soil particles.

Note that in order to obtain essential nutrients (cations) from soil a plant must pump out H⁺ ions. These H⁺ ions are swapped for the cations (such as K⁺ and Ca²⁺). For an excellent, short video on the Cation Exchange process between plants and soil/soil pore water (and the influence of soil texture) – see here. More on the influence of soil texture is available via the short video linked here.

Interestingly, the video explaining Cation Exchange linked above states that the vast majority of cultivated soils are negatively charged but some soils, mostly in the tropics, are positively charged. We’re in the tropics – so which soils are positively charged? The answer is those soils that are ancient and that have been subjected to intense and deep weathering over a long period of time. As a result of prolonged, intense weathering clay minerals disintegrate, losing their silicon (Si) in the process. As a result, the weathered soil has a lower negative charge (and may even have a positive charge), and thus a lower CEC. This reduced CEC is one of the reasons why lateritic soils in the tropics are less fertile than their younger, less intensively weathered counterparts in more temperate latitudes.

Increased acidity (increased concentration of H⁺ ions) results in many more H⁺ ions in the soil pore water competing with dissolved cations for attachment sites on soil particles. Because the H⁺ ions are generally more reactive they tend to attach to vacant attachment sites on soil particles and displace already attached cations of, for example, heavy metals. The latter are then dissolved in the soil pore water where they are much more biologically available, and can be taken up by plants through their roots. In solution, heavy metals such as Aluminium (Al) bind with phosphorus fertilizers (generally in the form of Phosphate, PO₄), forming – for example, AlPO₄, which is a form of phosphate that plants cannot use (cannot take up). Hence fertilizer applications to acid soils are often ineffective, and farmers must first find a way of neutralising the acidity (generally by liming, the application of quicklime, CaO).

The pH of solution also influences solubility of heavy metals. Generally heavy metals are in solution in acidic water. At higher pHs (strongly alkaline), the OH^– ions bind with the heavy metal cations forming solid compounds, which precipitate-out (they form “precipitates”). Varying the pH of wastewater, reservoir water etc entering water treatment plants is the main way of removing heavy metals from large volumes of water that are then used for human consumption, irrigation etc., as mentioned in an earlier lecture.

 

I’ve been enjoying reading my copy of Eleanor Herman’s excellent book “The Royal Art of Poison: Filthy Palaces, Fatal Cosmetics, Deadly Medicine, and Murder Most Foul“, a review of which can be found here. Chapter 3 “Dying to be Beautiful  Dangerous Cosmetics” has been particularly fascinating, in part because in addition to some rather startling revelations about the lengths people went to in the past to make themselves what they and others at the time considered beautiful, and then stay beautiful, the chapter also raised some questions that are relevant to GE3246. One of these is whether we are any more knowledgeable now about the true personal and wider costs of our luxury consumption. Luxury consumption is geared to meeting our wants, rather than our needs. Luxury consumption is largely avoidable (it is not necessary) – but it also involves the use of valuable resources (including energy, water etc) in their production and transport, thereby denying others of those resources, and generates pollution. Everything we consume causes pollution- it comes with embodied pollution, in other words. In some cases, our luxury consumption actually does us harm. Certainly the problems it causes – often in distant parts of the world – can end up causing food insecurity, water shortages, harmful pollution etc for others. But more about all that later in GE3246 ….

Back to The Royal Art of Poison. You can actually view a short and very enjoyable video summary of Chapter 3 of Eleanor Herman’s book here. I enjoyed the account (in the book) of how Queen Elizabeth the First (QE 1), who died at what was then the ripe old age of sixty-nine in 1603, had led a generally healthy life, at least according to standards at the time. For a member of royalty, she ate healthily and exercised often ~ she was, apparently, fearful of ending up like her father, the morbidly obese King Henry VIII. Unfortunately QE 1 contracted smallpox during her 20s, and this left scars on her body and face. Not only were blemishes considered unattractive at the time, they were also considered “proof of God’s displeasure” – even manifestations of sexual urges and desires. QE 1 seems to have been so-encouraged to apply, liberally, a ceruse, a pigment that contained highly poisonous white lead and often arsenic too, to cover her blemishes. Unfortunately the lead leached into the body through the skin, and this is thought to have caused QE 1 to lose her hair, become less active (lead poisoning causes muscle paralysis) and to suffer declining metal acuity and major swings in her mood. It also likely corroded her skin, causing QE 1 to have to apply even more ceruse, thus kick-starting a positive cause-effect-cause cycle involving ever thicker applications of ceruse. Herman argues that rather than simply aging, heavy metal poisoning may have contributed to mood swings, odd decisions (such as to have her friend Robert Devereux executed) and depression that characterised the last years of QE 1’s life, and ultimately her death.

Herman describes other cases, a notable one of which is that of Diane de Poitiers, the mistress of French King Henri II, who died in 1566. De Poitiers was commonly regarded as one of the most beautiful women of her time. She went to extraordinary lengths to stay youthful looking, including bathing in assess’ milk, to remove body hair and prevent the signs of aging, and taking an elixir that was meant to promote a youthful complexion. The elexir contained gold – and gave a person who drunk it a white skin because the gold caused anemia. Gold is a heavy metal and anemia can be caused by heavy metal poisoning. The elixir that De Poitiers took was meant to be used sparingly ~ no more than once a month (even back in the 16th century people knew that excessive use was not good for you), but it is thought that De Poitiers took the elixir once a day over many years. She accumulated so much gold from the elixir that when her remains were discovered centuries later the soil in which she had been buried was heavily contaminated with gold that had leached from her body as it decayed!

Of course, we’re much more mindful consumers these days – aren’t we? I am not sure that we are. We still use urine in face creams (pee is a great moisturiser, apparently) just as folk did in the 16th century, and heavy metals (e.g. titanium dioxide) in sunscreens and other cosmetics. And botox injections are popular. These involve injecting a toxin produced by the gram positive bacterium Clostridium botulinum. The same toxin causes the potentially fatal illness Botulism.  Botulism through normal routes (e.g. food poisoning – especially from eating fish that has not been properly stored or cured/fermented and canned foods that have “gone off”) is now relatively rare. Although we are told that the cosmetic use of botox is generally safe, because of the relatively low concentrations used, different people are likely to have different levels of sensitivity, and deaths do occur (including one in Singapore earlier this year – see here).

For an excellent account of current cosmetic use – and the toxins involved, many linked to petrochemicals – see the short video here. The video “examines the pervasive use of toxic chemicals in our everyday personal care products, from lipstick to baby shampoo” and is by The Story of Stuff Project, a project dedicated to mindful consumerism and de-materialisation.

Perhaps if we are willing to risk our own health through our luxury consumption we shouldn’t be surprised that we are also willing – at the same time – to risk the health of our planet.

A more mindful approach to consumerism would seem to be needed – perhaps urgently. There is now guidance out there to help us to be more mindful, or literate, consumers. See, for example, the Campaign for Safe Cosmetics webpage.

 

Several news agencies are today reporting research that appears to suggest that, in addition to everything else, air pollution may cause (or contribute to) baldness. More precisely it seems that fine particular matter in the air that we breathe may cause hair loss. One article goes further and suggests that men living near busy roads are particularly vulnerable!

The American Association for the Advancement of Science (AAAS) is also reporting the finding through its EurekAlert! website ~ see here.

The research described was presented at the 28th EADV Congress in Spain earlier this week and found that fine particulate material in the air can interfere with a body’s production of proteins (β-catenin, cyclin D1, cyclin E and CDK2) that are responsible for hair growth and hair retention.

The lead researcher on the study, Dr Hyuk Chul Kwon (Future Science Research Centre, Republic of Korea) opined “[w]hile the link between air pollution and serious diseases such as cancer, COPD [Chronic obstructive pulmonary disease] and CVD [Cardiovascular disease] are well established there is little to no research on the effect of particular matter exposure on the human skin and hair in particular. Our research explains the mode of action of air pollutants on human follicle dermal papilla cells, showing how the most common air pollutants lead to hair loss”.

Recent reports have drawn attention to the poor quality of air in many cities and regions globally. Poor outdoor (ambient) air quality results in around 3 million premature deaths annually, and is particularly a problem in the eastern Mediterranean, Southeast Asia and the Western Pacific (WHO 2016).

Air Quality Indices (AQIs) are communication tools that are now relied upon in many parts of the world to disseminate information on both outdoor air quality (or more accurately the level of one or more pollutants in outdoor air) and the associated risks posed to public health. Generally, reported AQIs relate to average air quality over the previous 24 hours. The idea is that average air quality over that period provides an indication of likely conditions in the near future, and therefore a basis for people to settle on their planned activities for the day ahead.

Estimates of AQI are based on measurements of a limited number of reference (or Criteria) air pollutants, with each pollutant having their own Air Quality Standard (AQS). Most AQI are determined from the concentrations of six Criteria pollutants: sulphur dioxide (SO₂), particulate matter (PM₁₀), fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), carbon monoxide (CO) and ozone (O₃).   Variety exists between countries in the AQI adopted (for a useful review of single- and multiple-pollutant indices, see Plaia & Ruggieri 2011). This can make inter-country comparisons of air quality, expressed through AQI, difficult. Figure 1) shows the effect of applying different AQI methodologies to the same set of air pollution data, in this case for Portugal.

Figure 1: AQI for Portugal on15 December 2015 calculated using the same air quality data but according to the different AQI methodologies in use in Portugal, the USA, China and Germany (from Monteiro et al. 2017).

Some geographic variation is understandable, because the importance of particular pollutants is likely to vary between locations. Levels of heavy metals, for example, may be much less of an issue away from built-up areas, main roads and industrial developments. For this reason, levels of lead (Pb) in the atmosphere are considered in the calculation of AQI in some cities in India (Monteiro et al. 2017).

Similarly people are expected to react differently to the same mix and intensity of pollutants. Indeed, links between the concentration of a pollutant (the range in levels of pollutants between “breakpoints”), particular categories of health warning (moderate, unhealthy, very unhealthy etc) and the associated range of activities advised (unusually sensitive people should reduce prolonged or heavy exertion, sensitive groups should reduce prolonged or heavy exertion etc), often involving the use of bright colours, characterising AQI are less straightforward than they might initially seem. For example, there is likely to be a great deal of variation in sensitivity to air pollutants even among people classed as sensitive. In addition, there are no safe levels of atmospheric concentrations of particulate matter (PM₁₀ and PM_2.5) or ozone (O₃); research has not been able to identify thresholds of these three Criteria pollutants below which adverse effects do not occur (WHO 2006). Furthermore, pollutants do not tend to act in isolation, yet little consideration is given in many AQIs to the effects of air pollutants as part of a mix of chemicals (Bishoi et al. 2009). Concentrations of air pollutants are a form of compositional data. The data are often incomplete, and this can compromise the value of AQIs, especially those based on the concentrations of individual pollutants. Because of this, Jarauta-Bragulat et al. (2016) suggest an alternative way of determining air quality in which AQI is established based on the geometric mean of the concentration measurements of all of the Criteria pollutants.

Cheng et al. (2007) describe the evolution of the current AQI in the US in response to increasing concerns regarding the health effects of air pollution. Originally established by the US EPA as a Pollution Standards Index (PSI) in 1976, the PSI was revised and renamed the Air Quality Index (AQI), and subsequently implemented, in 1999. The US EPA PSI ranges from 0–500, with 100 equal to the National Ambient Air Quality Standards (NAAQS), and was calculated for every pollutant that at the time had a NAAQS. The AQI also includes breakpoints for O₃ and fine particulate matter (PM_2.5), and divided the original index range 101–200 into separate categories (101–150 and 151– 200). These modifications aimed to strengthen the health information provided. Both the PSI and subsequently the AQI are relevant for a given time and location, and equate to levels of the pollutant that most exceeds its NAAQS (known as the Primary Pollutant). As a result, they may under-estimate the true health effects of air pollution.

Table 1 (upper & lower): US EPA AQI breakpoints and corresponding colour codes (from Jarauta-Bragulat et al. 2016).

China has been monitoring ambient air quality since the 1980s (Chen et al. 2016), i.e. far longer than many nations. A simplified (compared with present day) Air Pollution Index (API) has been reported on a weekly basis since 1998, with additional pollutants (including PM₁₀) added in 2000. In 2012 the API in China was expanded again, to include CO, O₃ and PM_2.5. In January 2013 China also started reporting air pollution levels according to AQI, with the latter based on new NAAQS (Table 2), making comparison between the API and the AQI difficult. As with the US EPA AQI, China’s AQI is not based on the full suite of Criteria pollutants measured, but on the Primary Pollutant, or in this case the pollutant that most exceeds its equivalent to an IAQI = 50 (values in the top row of data in Table 2). Days where pollution levels do not exceed AQI = 100 are known as “attainment days”. The number of attainment days (or “blue sky” days in Beijing) is regarded as a key indicator of urban air quality in China (Chen et al. 2016).

Table 2: Concentration limits (breakpoints) for AQI calculation in China (from Chen et al. 2016)

Public awareness of air pollution, and in particular the potential detrimental health impacts of poor air quality, has also risen dramatically in Singapore in recent years, in line with much of the rest of the world. While the National Environment Agency (NEA) in Singapore has long collected air quality data, these data have only relatively recently been made available to the general public. Singapore’s Pollution Standard Index (PSI) is based on the US EPA PSI (later AQI). The Singapore PSI runs from 0-500, and involves the measurement of concentrations of six Criteria pollutants: SO₂, PM₁₀, PM_2.5, NO₂, CO and O₃. Fine particulate matter (PM_2.5) was only considered as part of the PSI from August 2014, although according to Velasco & Rastan (2015), PM_2.5 measurements – collected at one-hour intervals – were measured from long before that date.

Determining Singapore’s PSI involves the same process as the US EPA AQI and China API/AQI in that the actual measured concentration of each of the six Criteria pollutants are used to generate a sub-index value for that pollutant, based on the breakpoints shown in Figure 2 and Table 3 (lower). As with the US and Chinese systems, the PSI is not based on the full suite of Criteria pollutants measured, but on the Primary Pollutant. Moreover, during major haze events (as determined by the NEA), the Primary Pollutant is PM_2.5.

Table 3 (upper & lower): NEA Singapore PSI breakpoints and corresponding colour codes (from NEA website. Detailed information on breakpoints available here)

Historical PSI data are available for Singapore from 1 January 2010 (reading once per day at 4pm, then 3x per day from 24 August 2012 (8 am, 12 noon & 4pm)), but only for one location on the island.  Since 20 June 2013 data have reported hourly for five locations in Singapore and are available via here. Since April 2014, PSI determinations have potentially included PM_2.5. One consequence of the current arrangement is that it is difficult to carry out analyses of long time series of past air pollution measurements in Singapore, or to compare long term variations in air quality with neighbouring countries or indeed with other nations in Asia and farther afield. This creates problems for the analysis of, for example, the impacts of past severe deviations in air quality, and therefore our ability to anticipate the effects of projected future variations.

Figure 2: Graphical representation of the relationship between AQI and concentrations of four Criteria pollutants, based on the US EPA method. Note (1) circles = break points and (2) a linear relationship is assumed between break points.

A common source of confusion in Singapore is why the PSI for the country reported by the NEA is often different from AQIs also reported for SIngapore by other organisations, such as PM haze, IQAir (a company that supplies air filter equipment!) and aqicn? Part of the reason is that some organisations (e.g. IQAir, aqicn) also make use of data from sources that may not be fully reliable (e.g. private, off-the-shelf pollution monitoring equipment that may not be properly maintained/calibrated). The main reason is, however, that the PSI is reported by the NEA on the basis of a 24-hour moving average (average air quality), whereas other organisations report AQIs based on hourly-averaged or single point data. Reporting the PSI in terms of average air quality smooths out short-lived increases in pollution levels and provides a measure that is comparable with World Health Organisation (WHO) air quality guideline values. For example, according to WHO (2006), annual and 24-hour mean values for PM_2.5 should not exceed, respectively, 10 and 25 ug m^–3 . However, those same short-lived excursions in air pollution levels can result in negative health effects for some people, especially those suffering from existing respiratory and cardio-vascular ailments.

Pollution in urban areas is known to vary greatly not only through time but also spatially. Urban pollution has a geography, with some areas (e.g. bus stops, major road junctions) associated with far higher levels of air pollutants known to be detrimental to human health than others. The current NEA network of five monitoring stations that provides estimates of PSI for the general public is unlikely to capture this spatial variability. This might become a cause of greater concern once confusion over how AQIs/PSIs are arrived at is resolved. A recent study during a haze-free period determined PM_2.5 concentrations in roadside locations in Singapore (28.88 ± 5.92 ug m-3) well above both annual and 24-hour mean WHO guideline values (Zhang et al. 2017). Prolonged exposure to PM_2.5 concentrations around 30 ug m-3 is similar, in health impact terms, to smoking passively around 15 cigarettes per day, according to research carried out in the Netherlands (van der Zee et al. 2016).

Recent developments in air pollution monitoring and mobile communications technology could provide an answer – and help shift responsibility for monitoring air quality from government and private organisatons to the general public. For example, bicycle and scooter schemes are common in many cities, Bikes and scooters could be equipped with equipment that can be used to monitor pollutants that are representative of other, more difficult to measure pollutants, with measurements relayed to members of the general public through their mobile phones. Thus equipped, members of the general public could then use the information to plan their journeys to work/school, recreational activities etc avoiding the most polluted routes. This is not as far-fetched as it seems – see for example Appmosfera. Easy access to high spatial and temporal resolution AQI information is likely to be an important part of ensuring livability in our smart cities of the future.

References

Bishoi et al. (2009) A Comparative Study of Air Quality Index Based on Factor Analysis and US-EPA Methods for an Urban Environment. Aerosol and Air Quality Research 9: 1-17

Chen, W. et al. (2016) Urban air quality evaluations under two versions of the national ambient air quality standards of China. Atmospheric Pollution Research 7: 49-57

Cheng, W.L. et al. (2007) Comparison of the Revised Air Quality Index with the PSI and AQI indices. Science of the Total Environment. 382: 191-198

Jarauta-Bragulat, E. et al. (2016) Air Quality Index revisited from a compositional point of view. Mathematical Geosciences 48: 581-593

Monteiro, A. et al. (2017) Towards an improved air quality index. Air Quality, Atmosphere & Health 10: 447-455.

Plaia, A. & Ruggieri, M. (2011) Air quality indices: a review. Reviews in Environmental Science and Bio-technology 10: 165-179

Van der Zee, S.C. et al. (2016) Air pollution in perspective: health risks of air pollution expressed in equivalent numbers of passively smoked cigarettes. Environmental Research 148: 475-483

Velasco, E. & Rastan, S. (2015) Air quality in Singapore during the 2013 smoke-haze episode over the Strait of Malacca: lessons learned. Sustainable Cities and Society 17: 122-131

WHO (2006) WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide. Global update 2005. Summary of risk assessment. WHO Press, Geneva, Switzerland, 22 pp

WHO (2016) Ambient air pollution: A global assessment of exposure and burden of disease. WHO Press, Geneva, Switzerland, 131 pp

Zhang, Z-H. et al. (2017) Characterization of traffic-related ambient fine particulate matter (PM2.5) in an Asian city: Environmental and health implications. Atmospheric Environment 161: 132-143

 

In the next GE3246 Environmental Pollution lecture (Lecture 6) we will discuss freshwater pollution. In particular, we will cover two processes that commonly impact freshwater ecosytems ~ acidification and eutrophication. As mentioned previously, both processes occur naturally. Human activities have, in effect, brought about an acceleration in both. To distinguish human-accelerated acidification and eutrophication from natural, background, levels we on occasion talk about “cultural acidification” and “cultural eutrophication”. Also as mentioned already, both acidification and eutrophication impact environments globally – aquatic and terrestrial.

We will not have time in the lecture to go into great detail regarding the freshwater effects of acidification and eutrophication. I have already covered ocean acidification in a previous post and in the last lecture (Lecture 5). I have also, briefly, mentioned eutrophication – or enrichment of an ecosystem by nutrients, in particular nitrogen (N) and phosphorus (P) – in past lectures. Under natural conditions, most ecosystems – including freshwater bodies – are nutrient limited. Human activity changes that, however, by making available enhanced levels of nutrients. This results in more primary productivity, which upsets the trophic and chemical balance, and this can cause problems for aquatic organisms and for other organisms, such as humans, who might be dependent on the services provided by the impacted ecosystem.

Excess N and P entering streams, rivers and lakes (including reservoirs) is generally from agricultural runoff (e.g. the wasteful application of fertlizers, which contain N and P) and sewerage (e.g. ineffective waste treatment facilities, broken septic tanks). Run-off from urban areas also often contains high levels of nutrients. Recreational areas, notably golf courses, are also sources of nutrients entering water bodies. As many freshwater ecosystems are connected (drain eventually) to the sea, excessive nutrients from the land also cause eutrophication in coastal areas. Red tides are one consequence of eutrophication of coastal waters.  Red tides area a form of Harmful Algal Bloom (HAB). HAB is a bit of a misnomer, because HAB do not just involve algae, they also involve certain forms of cyanobacteria. The error is forgivable, because cyanobacteria used to be known as blue-green algae! HAB deplete oxygen (O) in the water column, effectively suffocating other organisms. Following their death a rupturing of their cells releases toxins, and these toxins can kill aquatic taxa such as fish (e.g. fish that are being farmed in the same waterbody) and be passed on to humans who eat the contaminated fish (Paralytic Shellfish Poisoning (PSP) caused by the neurotoxim saxitoxin can be fatal to humans) . HAB can also directly effect the health of humans in other ways too, e.g. Diarrhetic Shellfish Poisoning (DSP) can as the name suggests cause sub-lethal ailments associated with stomach problems.

For an excellent review of HAB in tropical aquatic environments, see: Tropical Cyanobacterial Blooms: A Review of Prevalence, Problem Taxa, Toxins and Influencing Environmental Factors. The co-authors of the article include Darren Yeo, who some of you might know from the Department of Biological Sciences at NUS.

Most attention on the impacts of eutrophication focuses on the aesthetic (eutrophic water bodies are often unsightly and smelly places!) and direct health (e.g. PSP, DSP) effects. There are other consequences, however, one of which is a link to the emergence of infectious diseases. The paper by Johnson et al (2010), titled “Linking environmental nutrient enrichment and disease emergence in humans and wildlife”, is available in an open access form (hence I can attach it to this blog – below). Johnson et al. link environmental eutrophication to an increased occurrence of diseases such as malaria. They conclude that “available evidence indicates that ecological changes associated with nutrient enrichment often exacerbate infection and disease caused by generalist parasites with direct or simple life cycles. Observed mechanisms include changes in host/ vector density, host distribution, infection resistance, pathogen virulence or toxicity, or the direct supplementation of pathogens. Collectively, these pathogens may be particularly dangerous because they can continue to cause mortality even as their hosts decline, potentially leading to sustained epidemics or chronic pathology. We suggest that interactions between nutrient enrichment and disease will become increasingly important in tropical and subtropical regions, where forecasted increases in nutrient application will occur in an environment rich with infectious pathogens”.

Complaints about the complacency of youth are common place, yet millions of people around the world – led by the world’s youth – are in the process of raising attention about climate change and its impacts. Today Singapore joins that effort though the SG Climate Rally.

Climate change is an effect – perhaps the greatest effect – of environmental pollution ~ in this case the wasteful release of CO2 and other greenhouse gases to the atmosphere. As with other forms of pollution, the problem is best dealt with at source. We need to reduce emissions and find ways of protecting and enhancing existing carbon stocks that do not jeopardise food and water security, biodiversity conservation etc while also protecting the most vulnerable. To do this we all have a contribution to make, irrespective of age.

 

I think most people are now concerned about the health impacts of air pollution. In lecture # 7 and tutorial # 3 of the GE3246 module we will focus on air pollution and its health effects (and also on how those health effects are determined/quantified). We have, of course, already touched on the subject in our discussion of measuring and monitoring variations in pollution, and in particular air quality indices (AQIs).

Most of the concern regarding air pollution is, understandably, on the effects on the health of people exposed to polluted air. In most rich parts of the world we can still choose whether to drink polluted water (although this has not been the case in Flint, Michigan, US, since 2014 in what has become known as the Flint Water Crisis) and we’re perfectly happy to discard food that is past its eat-by date because it might have “gone off” and be contaminated (or “spoiled”) by bacteria etc. However, even in economically wealthy countries such as Singapore we have little choice but to breath the air that is all around us, or ambient air (although we can filter the air, so long as the masks etc are available and we can afford to purchase them). But what about the unborn? Should we also be concerned about the effects of air pollution on foetuses – our yet to be born offspring?

Recent research published on 17 September 2019 in Nature Communications suggests that we should be concerned about the effects of air pollution on our unborn children. The Nature Communication article is open-access, but I have also uploaded a copy to this blog (see below). The research is being reported widely – see for example a report in the Guardian newspaper and on the Live Science website. The latter also includes a link to a short video on urban air pollution, and how urban air pollution levels have a high focality (they vary greatly over relatively short distances). The video features researchers and research from University of Texas, Austin, US. It is worth a watch!

Basically the work published 17 September 2019 in Nature Communications found particles of black carbon – part of the fine particulate matter that is released on combustion of biomass, in the form of fossil fuels but also in the form of extant peatlands and forest – on both sides of the human placenta. In other words, fine particulate matter was able to pass from the maternal side of the placenta to the foetal side. Moreover, the number of particles found on the foetal side of the placenta varied in accordance with the concentration of particles in the air that the mother had been exposed to while pregnant – in other words, the greater the level of air pollution during pregnancy then the greater the number of particles found on the foetal side of the placenta.

We can of course speculate on the health effects of exposure to extremely small black carbon particles from a very early age (even from before a person is born!). You can, for example, watch a short video titled “Smog in our brains” in which Dr. Jennifer Weuve, an Assistant Professor of internal medicine at Rush Medical College in the US, discusses the effects of particulate air pollution on the brain. The authors of the study recently published in Nature Communications conclude their article by saying “[t]he evidence of particle translocation to the placenta might be a plausible explanation for the observed detrimental effects of ambient particulate air pollution on fetal development over and beyond the increased maternal systemic inflammation in response to particulate accumulation in the lungs”. They go on to cite the findings of research published in 2016 in the Journal of Physiology on the effects of ingesting very fine particulate matter (nanoparticles) on different stages of human development, from the foetus to adult. Nanoparticles can be smaller than even our most sophisticated air pollution measuring equipment is able to measure (i.e. smaller than PM2.5), but just because we cannot measure it, conveniently or otherwise, does not mean that it does not exist!

 

Mercury is a highly toxic element that is found both naturally and as an introduced contaminant in the environment. Although its potential for toxicity in highly contaminated areas such as Minamata Bay, Japan, in the 1950s and 1960s, is well documented (e.g. see here), research has shown that mercury can be a threat to the health of people and wildlife in many environments that are not obviously polluted. The risk is determined by the likelihood of exposure, the form of mercury present (some forms are more toxic than others), and the geochemical and ecological factors that influence how mercury moves and changes form in the environment.

The toxic effects of mercury depend on its chemical form and the route of exposure. Methylmercury [CH₃Hg] is the most toxic form. It affects the immune system, alters genetic and enzyme systems, and damages the nervous system, including coordination and the senses of touch, taste, and sight. Exposure to methylmercury is usually by ingestion, and is absorbed more readily and excreted more slowly than other forms of mercury. Elemental mercury, Hg(0), the form released from broken thermometers, causes tremors, gingivitis, and excitability when vapors are inhaled over a long period of time. Although it is less toxic than methylmercury, elemental mercury may be found in higher concentrations in environments such as gold mine sites, where it has been used to extract gold. If elemental mercury is ingested, it is absorbed relatively slowly and may pass through the digestive system without causing damage.

Mercury in the environment can have natural sources, such as volcanic activity and the weathering of mercury-containing bedrock (e.g. biotite-rich granite). Mercury is also found naturally in oil, coal and gas reserves. Combustion of fossil fuels is therefore a major source of mercury entering the environment. As emissions from the combustion of fossil fuels are often to the atmosphere through tall chimney stacks etc, mercury can be transported over long distances before it is deposited in what may appear to be pristine sinks.

Methylmercury is formed through biomethylation. Methylation is the process through which methane is produced in the environment, and is associated with waterlogged, anaerobic conditions. Biomethylation is mediated by microbes that inhabit waterlogged, anaerobic conditions. An example of the microbes involved are sufate (SO₄)-fixing (or reducing) bacteria. They obtain their energy from breaking-off sulfur (S) atoms from sulfate compounds and then combining the S with another atom, such as hydrogen ~ the latter to form hydrogen sulfide (H₂S), which is a toxic gas that also gives rotten eggs their smell.

Biomethylation in the environment (see above) results in transforming certain heavy metals, such as arsenic and mercury, into much more mobile and biologically lethal forms. This is done by adding methyl (a compound formed of one carbon atom and three hydrogen atoms, CH₃) to the mercury atoms, to form CH₃Hg. We have already come across this problem in GE3246 – methylation is the process that increases the toxicity of arsenic in groundwater in countries such as Bangladesh, especially where that groundwater is contaminated by organic matter (e.g. sewerage). The conversion of inorganic mercury to methylmercury is important because its toxicity is greater and because organisms require considerably longer to eliminate methylmercury than non-methylated forms.

The concentration of dissolved organic carbon (DOC) and pH have a strong effect on methylation in the environment. Studies have shown that for the same species of fish taken from the same region, increasing the acidity of the water (decreasing pH) and/or the DOC content generally results in higher mercury levels in fish, an indicator of greater net methylation. Higher acidity and DOC levels enhance the mobility of mercury in the environment, thus making it more likely to enter the food chain.

The geography of biomethylation

Although mercury is a globally dispersed contaminant, it is not a problem everywhere. Problems of mercury toxicity are linked to biomethylation, and biomethylation as a distinct focality (or geography!). Aside from grossly polluted environments, mercury is normally a problem only where the rate of natural formation of methylmercury from inorganic mercury is greater than the reverse reaction. Environments that are known to favor the production of methylmercury include certain types of wetlands, dilute low-pH lakes, muddy, low energy coastlines etc. In other words, locations that are also often favoured by fish/shrimp farmers.

How does mercury enter the food chain?

People are exposed to methylmercury almost entirely by eating contaminated fish and wildlife that are at the top of aquatic foodchains. The exact mechanisms by which mercury enters the food chain remain largely unknown and may vary among ecosystems. As already mentioned, certain microbes play an important role in the production of methylmercury. These methylmercury-producing bacteria may be consumed by the next higher level in the food chain, thereby directly passing on the methylmercury they contain, or the bacteria may excrete the methylmercury to the water where it can quickly adsorb to plankton, which are also consumed by the next level in the food chain. Because animals accumulate methylmercury faster than they eliminate it (mercury ingested can take up to two months to be excreted), animals consume higher concentrations of mercury at each successive level of the food chain. Small environmental concentrations of methylmercury can thus readily accumulate to potentially harmful concentrations in fish, fish-eating wildlife and people. Even at very low atmospheric deposition rates in locations remote from point sources, mercury biomagnification can result in toxic effects in consumers at the top of these aquatic food chains.

Microplastics are now ubiquitously present in the environment – a news item on the BBC in August 2019 even described their presence in snow falling in the Arctic (“Why is there microplastic in Arctic snow?“)  Generally however when thinking about the detrimental environmental and ecological effects of microplastics our thoughts tend to focus on the world’s water bodies, and in particular its (our) oceans. Research published in the “early view” (or “ASAP”) issue of the journal Environmental Science and Technology ought to cause us to also think about the effects of microplastics on terrestrial ecosystems, including the terrestrial ecosystem that we rely upon for much of our food – soils!

Soils are a major – often largely ignored – sink for microplastics, much of it from the degradation of larger plastic objects. Researchers in the Applied Ecology Research Group of Anglia Ruskin University (ARU) in the UK have investigated the biophysical effects of different kinds of microplastics on soil structure and fauna, and on the productivity of perennial ryegrass under experimental conditions. Ryegrass is a group of grasses that are often grown for forage for animals, for preventing soil erosion and in ornamental lawns etc. The researchers at ARU found, for example, that the presence of conventional high density polyethylene (polyethylene is the most widely used substance in the manufacturing of plastic) in soil reduced the biomass of earthworms, led to a reduction in soil pH (increased acidity) and changed soil structure. The latter has implications for soil stability, or the ease at which a soil can be eroded.

Other forms of microplastic that are commonly released to the environment, including that made from polylactic acid, was associated with reduced plant (ryegrass) productivity. Polylactic acid is the basis for some “bioplastics”, which are degradable under certain conditions. Note that there is a difference between biodegradable and degradable – this difference with regard to polylactic acid-based plastics is highlighted here.

NUS students should be able to access the above article through the eJournals part of the NUS libraries website.