Not our own fate – but that of the chemicals we surround ourselves with in the modern world. So called environmental fate.
Every year the world produces around 19,000 tons of the toxic heavy metal cadmium, much of it for incorporation it rechargeable nickel-cadmium batteries or electronic components.
Global mercury production has been falling for years, but still stands at around 2,000 tons a year, used in fluorescent light tubes and thermometers.
Over a million tons of the chlorinated solvent tetrachloroethylene (PCE) is still produced every year, much of it used as dry cleaning fluid.
The pesticide Atrazine, though now banned in the EU and several other countries, is still one of the most widely used pesticides in the world, with around 70,000 tons produced every year.
In total the world produces many millions of tons of various chemicals every year – plastics, fertilizers, pesticides, electronic components, dyes, inks, medicines, fuels, detergents, solvents . . .
What happens to them all ? Where do they all go ? Where do they ultimately end up ?
Unfortunately, the answers are not always what we would wish for.
Obviously all these chemicals end-up somewhere – and the good news is that a proportion are recollected, recycled and reused. The bad news is this amount is still vanishingly small compared to the volumes produced.
What happens to the rest has has a lot to do with each chemicals mobility in the environment - some tend to helpfully stay put, but others easily dissolve into water and disperse more widely. An example is the unleaded petrol additive MTBE. Petrol itself is not very soluble, and tends to remain in place, but MTBE , is highly soluble and can easily disperse into groundwater following leaks and spills, and is responsible for contaminating many underground aquifers across the US and elsewhere.
Another important factor is how persistent each chemical is. Some will degrade or break down over time, while others may remain unaffected almost indefinitely. Usually, larger chemical molecules break down into smaller and less harmful molecules – like water or carbon dioxide etc, but sometimes, so called, break down products can be more toxic or more mobile than the original chemical. Dry cleaning fluid tetrachloroethylene (PCE), for example, can under some environmental conditions degrade into the far more toxic substance vinyl-chloride. Another example of global importance is the break down of the now banned pesticide DDT into it’s toxic, mobile and persistent decay products DDE and DDD - the impact of which led Rachel Carson to write her classic anti-pesticide book Silent Spring in the 1960s.
Once widely dispersed into the environment, substances often enter the natural food web – and may become increasingly concentrated by various biological processes, as organisms are unable to quickly metabolize or excrete a contaminant – leading to the build-up of ever higher levels. This is referred to as bioacculmulation, and is the reason many of us are now advised not to eat too much oily fish or lake and river caught fish, to avoid poisoning ourselves with mercury, PCBs or a variety of other chemicals.
Clearly not all chemicals are toxic, but the problem is that our systems for evaluating toxicity are not all that sophisticated, and often still rely upon poisoning mice in laboratories! Needless to say real world effects across multiple species can be very different. Additionally what is know as synergism can occur – where exposure to a particular chemical by itself might not be harmful, but in combination with another chemical, can result in toxic effects. This so called chemical cocktail effect is especially difficult to predict and evaluate – whether sex hormone effects, Gulf War syndrome or the possible effect of chemical mixtures in damaging species immune systems, making them vulnerable to previously harmless diseases.
Chemistry has built the modern world, and we all benefit from its advances – the device you’re reading this on, the clothes you’re wearing and whatever you’re sitting on – have all, most likely, been produced with the input of man-made chemicals. But unless we want the world to increasingly resemble a chemical soup, we need to get much better at preventing widespread release and dispersal of the chemicals we use.
The two most obvious things we could do are use less in the first place and get better at recycling those we do.
Something to bear in mind the next time you buy household cleaning products, or decide how to dispose of your used batteries or old light bulbs !
Photo by Jorge Franganillo, via Flickr