Cleaning up pollutants to protect future health

Abstract

Pollutants are everywhere. They can be found in the water that we drink, the air that we breathe and the food that we eat, and they are taking a toll on our health. In 2015, pollution was estimated to have caused almost 9 million deaths worldwide — three times more than those from AIDS, tuberculosis and malaria combined. Pollution can have a negative impact on health at any point in a person’s life. Often, the full effects are not seen for decades. Unborn babies and young children, for example, are especially vulnerable to the effects of methylmercury, a widespread pollutant that accumulates in fish and seafood and can cause intellectual disability and vision and hearing losses. According to a 2013 study (T. M. Attina & L. Trasande. Environ. Health Perspect. 121, 1097–1102; 2013), exposure to lead in childhood had a negative effect on IQ that resulted in an economic cost to low- and middle-income countries of around 977 billion international dollars (a unit of currency devised to account for differences in purchasing power between countries). And in the past two decades, evidence that exposure to particulates in the air are linked to dementia has begun to build. Part of Nature Outlook: The future of medicine Mercury, lead and air pollution are found throughout the environment. They are among ten pollutants highlighted by the World Health Organization as chemicals that pose a considerable threat to public health. The neurological problems that they can cause, for which treatment is often lacking, are especially concerning. “In the past decade, there has been a steady increase in the incidence of neurological disorders, and a great deal of these brain problems have been linked to exposure to different pollutants,” says Philip Landrigan, a paediatrician and epidemiologist in the Icahn School of Medicine at Mount Sinai in New York. Although the risks they pose are great, there is little understanding of the effects on health of many common chemicals. Since 1950, more than 140,000 new chemicals have been synthesized, of which around 5,000 are now ubiquitous in the environment. Despite people’s regular exposure to these compounds, a wide-ranging study led by Landrigan reported that fewer than half of these chemicals have been tested for safety or toxicity in humans. “The failure to test widely used chemicals for their potential toxicity represents a failure of governments to act on behalf of their citizens, and failure of the chemical-manufacturing industry to take responsibility for the products it produces,” he says. “We are conducting a massive toxicological experiment in the world today and our children, our grandchildren and future generations are the unwitting, unconsenting subjects.” The quest for evidence Before the health burden of pollution can be reduced, the compounds responsible must be identified. Researchers gather such evidence from two main sources. One is epidemiological studies that match exposure to a chemical — determined by its presence in the blood or urine — to the likelihood of developing a medical condition. The other is laboratory-based studies of a chemical’s effects in animals. Together, data from these sources represent the bulk of the evidence that is used to build a case against a pollutant, and to convince policymakers of the need to ban or restrict it. But the process takes time. “It takes over a decade for adequate toxicological and epidemiological data to be amassed to even begin making rational decisions about a chemical’s risk to human health,” says Jonathan Martin, a toxicologist at Stockholm University. In part, this is down to the interpretation of results. “Toxicological data can always be criticized because it is done in animals or cells with questionable relevance to humans,” Martin says. And even when an epidemiological study shows statistical associations between chemical exposure and adverse health effects, it cannot provide unequivocal evidence for causation on its own. As a result, vast amounts of data must be collected to build a solid case for removing a chemical from the environment, including findings made in a variety of species of animal. “Only when the toxicological effects that are observed in animals are the same ones that show up in humans in many large and well-constructed epidemiological surveys is there enough information to perhaps take regulatory action against a chemical,” says Martin. The building of evidence is therefore just the start of the journey down the long road towards a chemical’s withdrawal from use. Safe exposure Removing a pollutant from use entirely is difficult. Inaction by regulatory bodies is one issue that hinders the process. Lead — for many years, a common component of paint, water pipes and petrol — is now known to be highly toxic. In the past decade, thousands of studies have drawn links between lead exposure and the development of numerous health problems, including reduced cognitive function in children and adults. But although lead has now been banned in certain applications, evidence of its negative effects on health existed for many decades before policies on exposure were changed, even as safer alternatives were developed. “This long delay was the direct consequence of fierce opposition and incessant political lobbying by the lead industry,” says Landrigan.