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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.

 

Singapore’s online newspaper TODAY, produced by MediaCorp, carries an article today (14 September) that seeks to clarify confusion over which air quality index we should refer to when deciding whether to venture outside now that the haze is back. You can read the article here. I am not sure that I am any less confused having read the article.

I prefer to use a scale that matches air quality (and in particular the concentrations of small particles, or PM2.5) to the equivalent numbers of passively smoked cigarettes, published by van der Zee et al in 2016 in the journal Environmental Pollution. This scale assumes that there is no safe level of PM2.5.

Van der Zee is based in the Public Health Service of Amsterdam, Netherlands. He and co-workers determined that every 10 ug/m3 increment in PM2.5 corresponded to on average between about four to seven, passively smoked cigarettes per day. With PM2.5 concentrations in Singapore approaching 100 ug/m3 that equates to at least 40 passively smoked cigarettes. Let’s not forget that smoking in public places was banned because of the health risks of passive smoking.

 

Several news agencies, including the BBC, are currently reporting on the electricity power generation industry’s “dirty secret” ~ leaks of Sulphur hexafluoride, or SF6. SF6, a synthetic combination of one sulfur atom and six fluorine atoms, is commonly known as “deep voice” gas because of the effect that it has on the human voice. Its other properties are that it is inert, colourless, odourless, a lot heavier than air and does not conduct electricity. Because of the latter, it is used in the electricity power generation industry as an insulating medium to prevent electrical short circuits that can lead to fires and power outages.

Why is SF6 in the news at present? Well, it seems that as the world moves to smaller power generation plants – e.g. those associated with green (renewable) energy sources, the number of connections to the power grid increases. With that increase comes an increase in the number of locations where short circuits are possible, and hence a greater need for SF6. Why is that a problem? Well possibly as much as 15% of the SF6 used to prevent accidents in the power generation industry leaks out into the environment, where it is an extremely potent greenhouse gas. Just one kg of SF6 is equivalent to about 23,500 kg of CO2, and because SF6 is synthetic and inert it degrades very slowly, so emissions today are likely to be around for hundreds if not thousands of years.

Recently published research in the journal Energies (see journal article linked to this blog post) highlights the increased use of SF6 in the UK’s power generation industry, and the increased leaks as a result. Replicated across Europe, a similar rate of leaks equates to around 6.73 million tonnes of CO2 per year, or the emissions from 1.3 million extra cars on the road for a year. The use of SF6 is regulated in developed countries, but developing countries are under no pressure to regulate its use.

The generation of energy from renewable sources is an obvious improvement on relying on fossil and nuclear sources of power, but it also has its problems. Clearly the answer lies in finding ways of using renewable energy that are less wasteful of resources such as SF6 (how much energy does the synthesis of SF6 use?) in combination with reductions in the total amount of energy we use to live our daily lives (and therefore has to be generated). Another argument for economic degrowth as opposed to the current mindless fixation with ever-increasing, potentially planet-trashing GDP?

 

An item on the BBC website is today reporting on high concentrations of pollutants found in the skin and body fat (blubber) of bottlenosed dolphins in the English Channel. You can access the report here. The BBC report is based on an article that has only very recently been published in the journal Scientific Reports. The full article jn Scientific Reports is attached to this blog.

The pollutants include the heavy metal mercury and Polychlorinated biphenyls (PCBs), persistent organic pollutants (POPs) posing a serious environmental threat to wildlife and humans. PCBs were banned in many developed countries in the 1970s and 1980s (i.e.40-50 years ago), but they have persisted in the environment since the ban. You can learn more about PCBs here. Other chemicals were also found, including the residues of pesticides, in what the authors of the article refer to as a “cocktail of pollutants”.

Unfortunately it is not uncommon to find high levels of harmful pollutants in marine life, including in the fish that we eat. One killer whale found dead off the coast of Scotland was discovered to have “shockingly high” levels of PCBs in its body fat, while the health benefits of consuming fish can be undermined by high concentrations of heavy metals, such as lead, cadmium, arsenic and mercury, in the body fat of those same fish.

 

 

This coming Monday we will talk about ocean pollution. A current focus on plastic pollution in our oceans has – to some extent – caused us to forget about another major threat to our oceans, that of acidification.

Ocean absorb about 30% of carbon dioxide (CO2) that enters the atmosphere. As emissions of CO2 to the atmosphere increase, then the amount taken up by oceans (the size of the ocean CO2 sink, in other words) also increases. Oceans are therefore an important sink for anthropogenic (i.e. human) CO2 emissions. But what happens to that additional CO2 in oceans? Basically CO2 dissolves in sea water forming carbonic acid (H2CO3). Increased concentrations of carbonic acid reduce the pH (increase the acidity) of seawater. This increased acidity impacts other compounds and ecological processes, including the availability of carbonate ions (the building block for calcareous marine life, such as corals). For example the exoskeletons of corals are largely formed from aragonite, a form of calcium carbonate (CaCO3). We have know for some time that consumption of carbonate ions starves calcareous marine life of the material they need to grow (and, e.g., to keep pace with rising sea level) and to protect themselves from potential predators. Moreover the increased acidity can result in the dissolving of existing calcareous shells. So calcareous marine life faces two problems as a result of acidification – a shortage of carbonate to produce new shell material, and a weakening of their existing shells as a result of the increased acidity (reduced pH) of ocean water. Marine life faces other problems of course, including over exploitation,oceanic warming and pollution …. And not just pollution by plastic,  pollution by toxins such as heavy metals is also becoming an issue, as we will discuss in this coming week’s tutorials!

Early last year (2018) the Woods Hole Oceanographic Institution (WHOI), US, summarised the threat of ocean acidification on corals, focusing in particular on the link between ocean acifidication and the weakening of coral skeletons. Click here to view the article. Note that researchers at WHOI found that coral growth was much more complex than previously had been thought, and this complexity perhaps explains why some corals in some parts of the world are more vulnerable to ocean acidification than others. Basically what the researchers found was that the polyps – the tiny animals that form coral – were still able to produce aragonite at lower pH, but the aragonite was thinner, or weaker, because of an abundance of carbonic acid (HCO₃^–) ions relative to carbonate (CO₃^2-) ions in seawater. This results in corals located in exposed areas, where wave strength is greater, for example, being more vulnerable to damage than those corals in less exposed locations, even though the pH of the seawater might be similar.

Below you can watch an excellent, relatively short, documentary on the subject on ocean acidification, produced by the BBC and released in 2018. Australia gets a bit of a hammering in the documentary. The Great Barrier Reef is one of the world’s great coral ecosystems and is off the northeastern coast of Australia. Australia is one of the world’s largest exporters of CO2 emitting coal – in fact coal is Australia’s most valuable export ….

https://www.youtube.com/watch?v=Bxcq9QemIP0