The God Species_ How the Planet Can Survive the Age of Humans - Mark Lynas [86]
Some of the most troubling chemicals are the so-called “gender benders,” endocrine-disrupting substances whose effect is to mimic or block the action of natural biological hormones in an animal’s body. How exactly this effect takes place is still being studied, but some of the most notorious pollutants—DDT, lindane, organophosphates, PCBs—are thought to affect animal sexual biology, altering the reproductive capabilities of everything from bulls to alligators.4 The phenomenon was first noticed in England on the River Thames, where 30 years ago fishermen noticed that there was something wrong with the roach they were catching downstream from a wastewater treatment plant. The fish were neither male nor female but intersex: The male gonads contained both testicular and ovarian tissue.
Scientists suggested that “environmental estrogens” could somehow be to blame, by altering hormonal balances in the bodies of the fish and thereby affecting their sexual development.5 And sure enough, studies of the water composition found synthetic estrogen from the contraceptive pill (excreted by women in urine and not removed by sewage treatment) contaminating the river, along with horse estrogen used in human hormone-replacement therapy and alkylphenolic chemicals from cleaning agents and paints. In fact, aquatic animals seem to be particularly at risk from gender-bending chemicals. In the late 1980s it was discovered that tributyltin (TBT), a compound used in anti-fouling paints on ships’ hulls, was turning dog whelks “imposex” (male into semi-female and vice versa) all along the coast of the English Channel.6 Some female whelks were even found to be growing penises, blocking the release of eggs and rendering large numbers sterile.7
Another worrying property of man-made toxics is their capacity to accumulate in the food chain. Indeed, this propensity to “bioaccumulate” was recognized early on for DDT, which was affecting animals at the top of food webs apparently out of all proportion to their direct exposure. Many chemicals are also extremely mobile and can affect species a long distance away from their original site of release. Large quantities of the herbicide atrazine, commonly used on corn in the United States, fall out of the sky in rain or snow—and measurable quantities have been observed in precipitation in otherwise pristine national parks.8
Due to the dynamics of weather systems and long-range atmospheric transport, many of these toxics accumulate in the polar regions, particularly the Arctic. In 2009 scientists measuring contamination levels in the eggs of Norwegian and Russian ivory gulls discovered levels of pollutants—including DDT, mercury, PCBs, and brominated flame retardants—at unprecedentedly high concentrations, enough to potentially affect the reproductive success of the birds.9 The ivory gull population in the entire Arctic is thought to be only around 10,000, and studies in the Canadian Arctic show an 80 percent fall since the 1980s. In response to this decline, the gull has now been reclassified on the IUCN Red List from “least concern” to “near threatened.”10
Although PCBs were largely banned in producing countries by the end of the 1970s as their toxic potential became better known, these chemicals continue to accumulate in the Arctic. A recent survey of ponds near seabird colonies found high levels of PCBs in water nearest the bird-nesting and roosting sites, showing that toxic chemicals are still being transported to the far north via the marine food chain.11 Also at high levels was the poisonous