Tuesday, January 21, 2014
You may have heard that wastewater treatment plants can't remove all or even most of the pharmaceutical chemicals that pass through it, leaving trace amounts to flow into our rivers and lakes. And this is true. But it is also false. The real answer to the question of how well these plants remove pharmaceutical pollution is, "It depends."
A new study published in Environmental Science and Pollution Research is the latest in a long line of studies to show the nebulous nature of pharmaceutical removal. For this study, Chinese researchers Saichang Zhu and Hong Chen tracked the removal rate of 12 pharmaceutical and personal care products through two wastewater treatment plants that used different treatment techniques. Their 63 samples did reveal that neither facility adequately removed the whole suite of pharmaceuticals tested. But that is not to say that every pharmaceutical made it through the treatment process unscathed. And it also doesn't mean that removal rates were the same in both plants. In fact, their results showcase how exactly which chemicals are removed by which technology and by how much can vary dramatically.
For example, the treatment process at one facility–treatment plant A–removed more than 90 percent of caffeine, but the removal rate for ibuprofen and the antibiotic sulfamethoxazole was only around 64 and 33 percent. And the differences in removal rates were just as dramatic between treatment plants. Treatment plant A was only able to remove about 32 percent of the insect repellent DEET while a different process used at treatment plant B proved able to remove close to 80 percent.
More complicated still, Zhu and Chen's results revealed that the concentrations of some pharmaceuticals go up and down at different stages of the treatment process. Overall, both treatment plants removed moderate amounts of ibuprofen–about 65 and 52 percent. These numbers, though, came after a spike in the pain killer's concentrations during exposure to ultraviolet light, the final step at many treatment facilities. Most treatment stages break pharmaceuticals down into their bi-products, many of which we know little about. But the process can go the other way too. Exposure to ultraviolet light, it seems, triggers the bi-products of ibuprofen to reform into their parent compound, resulting in higher ibuprofen concentrations at the end of the treatment than there were at earlier stages in the process.
In addition to sampling at wastewater treatment plants, Zhu and Chen also examined whether running treated water through a man-made wetland system could reduce chemical concentrations even further. Here, again, treatment results proved inconsistent. The three-stage wetland system was able to remove more than 80 percent of the caffeine lingering in wastewater effluent, but the rate of removal was much lower for DEET, sulfamethoxazole, carbamazepine, and other chemicals. And, similarly to ibuprofen in the treatment facilities, concentrations of triclocarban–an antibacterial used in soap–actually went up in the final phase of treatment.
Read the full study to see a complete list of removal rates at the various treatment stages and learn about the risk levels of the pharmaceutical chemicals left in the effluent.
S. Zhu and H. Chen. 2014. The fate and risk of selected pharmaceutical and personal care products in wastewater treatment plants and a pilot-scale multistage constructed wetland system. Environmental Science and Pollution Research 21:1466-1479.