Every hour, an enormous quantity and variety of manmade chemicals, having reached the end of their useful lifespan, flood into wastewater treatment plants. These large-scale processing facilities, however, are designed only to remove nutrients, turbidity and oxygen-depleting human waste, and not the multitude of chemicals put to residential, institutional, commercial and industrial use. So what happens to these chemicals, some of which may be toxic to humans and the environment? Do they get destroyed during wastewater treatment or do they wind up in the environment with unknown consequences?
As Halden notes, over 4,000 chemicals in common usage in the US qualify as HPV chemicals, the vast majority of which have never been evaluated in terms of exotoxicity (their potential to adversely affect ecosystems), or for the risks they may pose to humans. "With each of these compounds, we are engaged in an experiment conducted on a nationwide scale," says Halden. "Odds are, some of these chemicals will turn out to be bad players and will pose problems for ecosystems, public health or both."