by Ian Cousins: Rainwater may be contaminated with chemicals, and scientists are still uncertain about their effects…
In many parts of the world, including Africa, people rely on rainwater as a source of drinking water, as well as for other household and livelihood uses. One of the reasons is water scarcity – sub-Saharan Africa has the largest number of water-scarce countries in the world. But there are concerns about how safe rainwater is to drink. It can be contaminated by dust and ash in the surroundings or by heavy metal from roofing material. Another concern is the presence of manufactured chemicals called perfluoroalkyl and polyfluoroalkyl substances (PFAS), or “forever chemicals”. As environmental scientist Ian Cousins and his team explain, they are a threat to the use of rainwater for domestic purposes.
What are PFAS and why should we be worried about them?
PFAS are a group of man-made substances often described as “forever chemicals” because they never break down in the environment.
They are found everywhere — in air, soil, and water as well as in wildlife, plants and humans. They can be found on the highest mountains, in the deep oceans and on both poles. A recent study highlighted the widespread presence of PFAS in rainwater, from the Tibetan Plateau to Antarctica, and noted that according to recently published health advisories, rainwater everywhere could be considered unsafe to drink.
According to the US Environmental Protection Agency, there are more than 12,000 of these chemicals in use. They have been produced and used on a large scale in a wide range of industrial and commercial applications since the second world war. Well-known uses include fire-fighting foams, non-stick cookware, and paper and board used to wrap and contain food. There are hundreds of uses, too numerous to list.
The human exposure pathways and health effects of most of the chemicals are poorly understood or unknown, except for four about which there is good information. They are: PFOS (perfluorooctanesulfonic acid), PFOA (perfluorooctanoic acid), PFHxS (perfluorohexanesulfonic acid) and PFNA (perfluorononanoic acid).
At elevated levels of exposure, these four have been associated with serious human health harms, including different forms of cancer, development toxicity, infertility and pregnancy complications, high cholesterol, ulcerative colitis, liver hypertrophy (“enlargement”), and thyroid disease.
The recent extremely low advisories for drinking water were prompted by the observation that exposure to these chemicals can lead to decreased vaccine effectiveness in children.
PFAS have been used for a long time. But intensive research on them began only about 20 years ago. Since then, the knowledge of toxicity has increased enormously. Based on this knowledge, the exposure level that is considered safe for humans has been set lower and lower.
The PFAS levels in health advisories for food and drinking water have been reduced to a point that is hard to achieve. This is because the advisory values are close to or even higher than the PFAS level in the environment.
In our recent study we showed that levels of certain PFAS in rainwater now exceed the guidelines set by the US Environmental Protection Agency even in the remotest regions of the Earth.
It is important to note that the levels of the four PFAS in rainwater and other environmental media have not increased recently. The use and emission of these so-called “legacy” PFAS was discontinued in many countries in recent years. But their stability means that they will remain in the environment indefinitely.