The God Species_ How the Planet Can Survive the Age of Humans - Mark Lynas [88]
Another myth is that other indicators of male fertility are also in worrying decline. These include hypospadias, a relatively common birth defect in males where the opening of the urethra is found not at the tip of the glans but along the underside of the shaft of the penis or even—in severe cases—in the scrotum, as well as cryptorchidism (the failure of one or both testes to descend into the scrotum in very young boys) and testicular cancer. Although some studies have shown hypospadias increasing in the U.S. and Europe over the last quarter-century,17 a great many more—using newer data—have shown no change at all,18 and it seems reasonable to conclude that there is no strong evidence implicating environmental chemicals in any change in male fertility in recent decades.
The same conclusion applies for women, too: A 2004 meta-study, for example, did not find any correlation between DDT exposure and breast cancer—both varied enormously among the sampled populations, but there was no relationship between the two.19 Another study in Long Island, New York, looked at breast cancer and pesticides, DDT, and PCBs in several hundred women but found no statistical link between those who suffered from cancer and those whose bodies contained the highest levels of putative toxics.20 None of this is to say that at more potent doses many of these compounds may not be toxic or carcinogenic, nor that they should not be strictly regulated in order to reduce the risk of health impacts. But at the very low levels most of us experience, the prevailing scientific wisdom is that they probably do us no harm at all.21
ENIGMATIC DECLINES
In the natural world, things are no less mysterious. For nearly a decade now researchers working in remote locations from Central America to Papua New Guinea have been finding dead or dying frogs, often strewn gruesomely around in scenes reminiscent of a field of battle. Sometimes only the skeletons remain, or just an empty pond, once teeming with amphibian life but now with scarcely a tadpole to be seen. Even where frog populations have not been utterly wiped out, many have been suffering an epidemic of strange deformities.22 Adults show up with two extra legs, misshapen eyes, or unpleasant skin lesions. Recent extinctions of entire species have been reported from Australia, Costa Rica, Honduras, Israel, Kenya, and Mexico. Many more are reported as “missing in action,” not sighted in the wild for several years and presumed extinct. The phenomenon is known as “enigmatic decline,” and environmental contaminants have been suggested as being at least partly to blame.
Laboratory studies have indicated impacts at very low concentrations of toxics, with worrying implications. For the herbicide atrazine, researchers at the University of California in Berkeley in 2009 performed an experiment in which male African clawed frogs were exposed to the chemical in water—at extremely low levels of 2.5 parts per billion, classified by the U.S. Environmental Protection Agency as safe for human drinking.23 Several of the atrazine-exposed male frogs were “chemically castrated” or “completely feminized” as adults, according to the subsequent report.24 This all sounds scary, even definitive, but the scientific rigor of the study has been questioned: Proper science demands that a reported conclusion can be independently replicated or repeated, but other studies on atrazine’s impact on the same species of frog have found no impact on growth or sexual development,25 and the idea remains extremely controversial.26
For amphibians in general, most scientists now believe that a fungal infection is the leading cause of declines and extinctions even in otherwise undamaged habitats,