by Aly Muhammad Ladak

source: Journal of Analytical Atomic Spectrometry

The idea of a mass poisoning event conjures up jarring images of accidental or targeted disasters. We tend to think of them as isolated tragedies – affecting one group of people in one location at a time. But with environmental toxicants, this is no longer the case – their impact reverberates across societies and the environment. One of the most striking examples of this is methylmercury, a compound that has poisoned animals, people, and entire ecosystems by accidental or negligent exposure. Its ability to cause harm across barriers – physiological, ecological, and societal – is symptomatic of a deeply interconnected world.

What makes methylmercury so dangerous? In short, its chemical structure lets it cross biological barriers that other substances wouldn’t normally be able to. Chemically, it consists of mercury with one or two attached methyl groups (-CH3, a small organic chemical compound). These organic groups allow methylmercury to mimic natural biological molecules, allowing it to cross barriers in the body and interfere with normal function. Its most pronounced – and most toxic – effects are neurological: by binding to a specific amino acid and mimicking a normal biological structure, it can pass unhindered across the blood-brain barrier. Once in the brain, these methyl groups are lost – so that the mercury that easily crossed the barrier into the brain can never leave. As a result, the mercury delivered by methylmercury can only accumulate in the brain, causing more and more damage to our neurons.

Mercury poisoning is often thought of as an old problem, a relic from times when the liquid metal was widespread in everyday products, from thermometers to batteries. In spite of this perception, mercury poisoning is a real and present threat today – especially with respect to methylmercury, which is the most common compound responsible for mercury poisoning. In fact, methylmercury is far closer to you than you might have imagined: you (along with almost every other person on the planet) have some amounts of it in your body right now. Since it doesn’t tend to leave organisms once it enters them, it builds up in each person’s body over their lifetime. Ultimately, the effects of mercury poisoning are not limited to the period of exposure – its accumulation in our bodies highlights that it can also cross barriers in time.

The persistence and widespread impact of methylmercury doesn’t just apply to humans – it can affect entire ecosystems, too. Methylmercury undergoes a process of bioaccumulation – it enters an ecosystem at the lowest level, and gets more and more concentrated as you move higher up the food chain. This spells out particularly bad news for us, since we are at the very top of the food chain. The first description of methylmercury crossing boundaries between species through bioaccumulation was in Minamata Bay, a Japanese fishing community. In the early 1950’s, the bay’s fish began dying en masse. Although it wasn’t known at the time, a factory was dumping methylmercury, a byproduct of some industrial chemical processes, into the bay. The effects weren’t limited to aquatic animals – cats and birds around the area began acting ‘drunk’, and many people of the surrounding community experienced the toxic effects of methylmercury poisoning for the rest of their lives. Therefore, methylmercury can cross barriers between species and across ecosystems.

From one age to another, from one species to the next, and from one society to its neighbors – the effects of methylmercury can be felt across barriers between societies. Sadly, marginalized societies are often forced to bear the brunt of the polluting actions of other societies. For instance, the Ontario First Nations community of Grassy Narrows has suffered from methylmercury poisoning due to outside forces. Dryden Chemical Company, a paper mill in the community, dumped mercury into the surrounding water. Bacteria can convert regular mercury into methylmercury, which then accumulates up the food chain until it reaches levels that are poisonous to humans. In response to the highly toxic leak by the paper mill, the federal government sent out a warning against consuming fish from that ecosystem, and has denied the majority of citizens’ claims for disability pensions. This completely ignores this society’s way of life – as they mainly live off fish from their surroundings – and it avoids holding the responsible parties accountable for the irreparable damage caused by their pollution. In short, settler-colonial society profited from, polluted, and abandoned this First Nations community – and methylmercury acted as the chemical medium for this process. 

Overall, methylmercury illustrates that environmental toxins cause harm across biological, ecological, and societal boundaries. Taken in the context of the global climate crisis, it serves as a stark reminder that failure to understand the interconnectedness between human societies and our environments can cause immense suffering and loss. 

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