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Did you know that there are almost 100,000 chemicals made by humans? Some of these are known to be highly poisonous (toxic). Many of these chemicals are deliberately poisonous because people use them for killing things - and have in times of war used some to kill each other. Some toxic chemicals bioaccumulateWhat does 'bioaccumulate' mean?It means that the toxic chemicals get concentrated in the bodies of animals which get eaten by bigger ones. Eaten, that is, with the toxic chemicals included. So the toxins increase in the big predators as they eat more contaminated prey. This can make them sick, or even kill them. It can also affect their reproduction so, even though they may appear healthy, they can't have babies so top predators like bears, dolphins and people can be badly affected.
Pollution is now such a big thing that it affects people and the animals, plants and complex web of life that humans depend on over the whole planet. For example, when people burn coal, mercuryWhy mercury is dangerousIt is a very poisonous heavy metal - as is lead - and it bioaccumulates in animals' bodies forms a small part of the waste gasesMostly the greenhouse gas CO2 which pour out of smoke stacks into the air. It then drifts around the planet, blown by the wind and eventually comes back to earth in rainfall, so it pollutes lakes and even the oceans. Like POPsPOPs: What are they?Persistent Organic Pollutants: DDT, PCBs and dioxins are examples, mercury bioaccumulates. Amounts of mercury in large predator fish can be over a million times that of the water they swim in. Not good for the fish or for people who may eat them. [More on mercury.]
Radioactive pollution is another concern, as some radioactive elements produced by nuclear power remain radioactive for thousands of years, though there are possible waysDealing with radioactive wasteWith new types of reactors, it will be possible to 'burn' the dangerous long-lived waste (actinides) and end up with a much smaller amount of waste. This will still be radioactive but the activity will die away in just a few hundred years of dealing with these.
Pollution also affects other planetary boundaries… for the worse. The aerosol boundary is tightly linked to pollution, both because aerosols are themselves pollutantsAerosols can make you sickSmoky aerosols like car and truck exhausts can cause asthma and because they carry pollution like mercury far and wide. And as some creatures have already been driven close to extinction because people have destroyed their homes, they will already be weakened. More pollution and more extreme climate events could tip them over the edge. And climate change means that more crop pests and diseases will migrateUnwanted migrantsJust as people migrate to find new and better places to live, so too do pests and diseases. Global warming makes it possible for these pesky organisms to survive and prosper where, until now, it had been too cold so farmers will end up using more pesticides… more pollution.
So how do the scientists decide how much pollution is too much? It's such a complicated subject that there is no simple way of setting up a planetary boundary. It may not be easy to tackle climate change but at least people know what the limits are for greenhouse gases. With chemical pollution, all that scientists can do is monitor what's happeningBioaccumulationSome chemical are particularly troublesome. These are the POPs: persistent organic pollutants such as DDT and polychlorinated biphenyls (PCBs) are the best known but there are many more. These, along with heavy metals like mercury, tend to become more concentrated higher up the food chain. Top predators like eagles, polar bears and humans can end up with so much of these toxins that their young can be damaged: eagles' egg shells become brittle and break; breast milk from humans and polar bears can be toxic to their babies to living things.
You can do your bit to help cut pollution. Have you read my Pollution Guide? There's some ideas for action at the end of it.