Next Monday is World Malaria Day, and DDT will surely be in the news. The usual parade of opinion pieces calling for a revival of DDT spraying to control malaria (as though it ever stopped) will be on display.
You'll likely also read that the World Health Organization (WHO) has raised fresh concerns about its safety, and you may even hear that the Stockholm Convention has endorsed its continued use. Let me try to explain what's going on.
When DDT was introduced more than 60 years ago, it initially scored victory after victory in the fight against malaria — nearly eliminating the deadly disease in many areas. But these wins were mostly short-lived, as mosquitoes rapidly developed resistance to the chemical. Today, its effectiveness is a fraction of what it once was; meanwhile an arsenal of better and safer anti-malaria interventions has been developed, including effective chemical-free strategies.
And so, under the auspices of the Stockholm Convention, the nations of the world have committed to phasing out DDT, while allowing it to be used in the short-term in those few places where it's still effective and other methods of malaria control are unavailable. This is an approach PAN enthusiastically supports.
Two studies came out in the last couple of weeks that really illustrate the problems associated with "PBT" chemicals: those which are simultaneously persistent, bioaccumulative, and toxic. Persistent substances resist degradation — you can move them around but it's really hard to get rid of them. Bioaccumulation happens when chemicals in food, water, and air end up getting stored in the body of a living thing. Thus, for a bass living in a mercury polluted lake, the mercury levels in the fish may be thousands of times higher than the levels in the water. A cow grazing on PCB-laced feed will store the chemical in her body and excrete it in her milk, and humans too act as sinks for all kinds of chemicals.