Toothpaste and toilet paper may not seem like the source of highly toxic chemicals, but a recent report suggests they are among a wide range of household products that put mercury into wastewater.
The study, by the Association of Metropolitan Sewerage Agencies, looked at discharges from four wastewater treatment plants across the nation — including one in the Bay watershed — to determine what levels of mercury were in wastewater discharges, and how much of that could be controlled.
The study was spurred by Great Lakes initiatives to phase out mixing zones for mercury and set an extremely low water quality criteria for mercury discharges — 1.3 parts per trillion — to protect wildlife.
“There was concern from the publicly owned wastewater treatment plants that even with their best efforts to control industries, there was still a good chance that we could not comply with that stringent of a water quality standard,” said James Pletl, environmental scientist with the Hampton Roads Sanitation District in Virginia, which was included in the study.
The study found that even when all industrial wastewater discharges were accounted for, there was a pervasive “background” level of mercury in wastewater treatment plant discharges, largely from minute quantities in everyday products and dental fillings, that would exceed the new standard by more than 100 fold.
Although the study was done for the Great Lakes, it raises questions about the achievability anytime soon of some of the Bay Program’s toxics goals, such as phasing out mixing zones and achieving a “zero release” of chemical contaminants.
“When you start talking about phasing out mixing zones, you’ve got to recognize that meeting some of these standards that are very, very low at the end of the pipe just may not be possible,” Pletl said. “Or if it is possible, it is going to be at a tremendous cost to the public.”
Estimates for the cost of end-of-pipe controls to remove residual amounts of mercury are about $10 million per pound removed, Pletl said.
And what is true for mercury is likely true for some other chemicals, he said. “Mercury is kind of the guinea pig for this kind of problem, but I don’t expect it to be the last one,” Pletl said. “This raises questions not only for the mercury parameter, but for other chemicals that occur at really low levels, as water quality standards become more and more stringent.”
Wastewater treatment plants can crack down on industrial dischargers, but the study concluded that a background mercury concentration of about 138 parts per trillion exists in municipal wastewater strictly from household wastes, which includes small amounts from a variety of sources.
The largest source, according to the study, is dental fillings, which account for about 85 percent of the background mercury. Minute amounts of mercury vapor given off by the fillings are absorbed by the body and later excreted.
But small quantities were also present in a wide range of household products, such as toothpaste, shaving cream, soap, toilet tissue, laundry detergent, bleach and drain cleaners, among other products.
The average household of two adults and two children generate about 14 nanograms of mercury a month through the use of mouthwash, 82 nanograms from shaving cream, 949 nanograms from soap, 5,912 nanograms from laundry detergent and 827 nanograms from toilet paper, the report said.
Although the amounts in individual products were barely detectable, they add up in the water system after getting washed down the drain, the report found.
That doesn’t mean there is no hope for reducing discharges stemming from such products. The report said that some of the background load may be reduced over time as products change and improvements in dentistry result in fewer cavities.