We’ve made it to the last “lesson” of this week! Let’s delve into the various disastrous ramifications of antifouling paint on animals, shall we? 

On the wild mute swan (Cygnus olor) – Turner and Hambling, 2012

The C. olor is found extensively across central and western Europe – you can spot them in the Singapore Botanic Gardens too! In Britain (where the study we are focusing on is located), there are approximately 30,000 to 40,000 individuals, where their numbers are rising steadily due to the ban of lead (Pb) we previously mentioned (thank god). 

How do heavy metals end up in them? They can end up in the habitat of the wild mute swan as metal-containing paint particles, or become bioaccessible by contaminating algae and sediments. The toxic heavy metals can thus enter the systems of the C. olor via the following ways:

• The accidental ingestion of metal-containing paint particles 
• The ingestion of contaminated sediment which settled on the submerged vegetation, and/or
• The ingestion of disturbed sediment while foraging for macrophyte (aquatic plant that C. olor feed on) or grit (to facilitate digestion in their gizzard)  

The study found that even with the phasing out of Pb in antifouling paint some 20 years ago, the remaining principal metals – Cu and Zn – continue to gravely threaten C. olor, with Cu being the most invasive. When in the system of C. olor, the paint pigments containing Cu and Zn leach because of the protons and chloride ions present in the gizzard. Let’s take a look at the chemical equations:

Cu poses the greatest threat to C. olor as it tends to form stable complexes with pepsin or organic anions (as opposed to Zn which gets re-adsorbed and precipitated in the intestines). The excessive ingestion of Cu can cause Cu toxicosis and critically high concentrations of hepatic Cu. For instance, swans living in a harbour were found to have black-discoloured livers with dangerously high dry weight Cu concentration of about 4,000 μg g−1. This is testament to the precarious situations C. olor are placed because of our poor, unregulated antifouling practices. 

On sea shell animals – Wang et al., 2008

How do heavy metals end up in them? Like with the C. olor, both Cu  and Zn can bio-accumulate in the internal organs of sea shell animals (e.g. clams, oysters, mussels). Here are the main ways: 

• Taking Cu as an example, Cu₂O (from the paint) oxidises in water to form Cu2+  which enter the larvas and spores. Cu2+ chelates with amino acid to form copper chelates, which bioaccumulate in the sea shell animals’ organs, or
• Microorganisms can grow on boat hulls applied with antifouling paint. Sea shell animals then attach onto the hulls, consuming Zn and Cu-containing microorganisms as their food, accumulating in their organs

Finally, on humans.

Heavy metals can bioaccumulate in our bodies, especially if our food is contaminated. Cu and Zn concentrations increase progressively throughout the trophic pyramid. This means that us, humans, who are on a higher trophic level, consume much greater amounts of heavy metals – via biomagnification. Here is a nice visual representation of biomagnification: 

The thing is, Cu and Zn are essential micronutrients for the human body (Lee, Chung & Lee, 2018). In fact, we need to absorb about 55 mg/d and 13 mg/d of Cu and Zn respectively (Wang et al., 2008). It is only when consumed in high concentrations that adverse effects such as hypothyroidism, night blindness and keratitis may surface (Lee, Chung & Lee, 2018). 

In China, the oyster is a popular traditional Chinese medicine with a myriad of uses, from controlling blood pressure, combating fatigue, to boosting the male reproductive system (Wang et al., 2008). However, are we doing ourselves more harm than good? After all, Cu and Zn concentrations in oysters from antifouling paint films in the Xiamen maritime spaces were revealed to be 12 and 5 times higher than those sold in markets (Wang et al., 2008)! This is perhaps an extreme example of the disastrous health effects of excessive heavy metal consumption, but in 1785, a woman suffered from Cu poisoning which induced vomiting, bellyaches and diarrhea. Eventually, she succumbed to her condition (Wang et al., 2008). 

Well, that was a grim note to end on… I hope no one has to ever go through that. 

Nevertheless, we hope that this week’s posts on antifouling paint and heavy metal pollution resulting from the consumerist culture have been enlightening in some ways. Thank you for sticking with us throughout these “lessons” ^-^ 

 

References: 

Lee, S., Chung, J., Lee, Y. (2018) Cu and Zn concentrations in seawater and marine sediments along Korean coasts from the perspective of antifouling agents. Bulletin of Environmental Contamination and Toxicology. 101(2), 185-190. Available from: https://doi.org/10.1007/s00128-018-2380-y. 

Turner, A. & Hambling, J. (2012) Bioaccessibility of trace metals in sediment, macroalga and antifouling paint to the wild mute swan, Cygnus olor. Water, Air & Soil Pollution. 223(5), 2503-2509. Available from: 10.1007/s11270-011-1043-y. 

Wang, J.L., Wang, F.Q., Yu, J. Zhuang, Y., Zhou, X.F., Zhang, X.B. & Peng, B.X. (2008) A survey analysis of heavy metals bio-accumulation in internal organs of sea shell animals affected by the sustainable pollution of antifouling paints used for ships anchored at some domestic maritime spaces.中国科学通报：英文版 53(16), 2471-2475. Available from:  10.1007/s11434-008-0355-9. 

Images: 

Facebook (2017) Clams (Spongebob Squarepants Episode). Available from: 

https://www.facebook.com/Clamsspongebobmrkrabsmemillionthdollar [Accessed 3 September 2020]. 

Tap Score (n.d.) Heavy Metals And Bioaccumulation: What You Need to Know. Available from: 

https://mytapscore.com/blogs/tips-for-taps/heavy-metals-bioaccumulation [Accessed 3 September 2020].