Triclosan is an active ingredient in many products claiming antibacterial properties. (Photo by Kinna Ohman)
After sewage is cleaned at a wastewater treatment plant, sludge is left behind. This
sludge is often used on farms as fertilizer. But the wastewater treatment doesn’t get
rid of all the drugs and chemicals we flush down the drain. Kinna Ohman reports
researchers are finding some of these chemicals are affecting wildlife and could be
getting into our food:
Transcript
After sewage is cleaned at a wastewater treatment plant, sludge is left behind. This
sludge is often used on farms as fertilizer. But the wastewater treatment doesn’t get
rid of all the drugs and chemicals we flush down the drain. Kinna Ohman reports
researchers are finding some of these chemicals are affecting wildlife and could be
getting into our food:
Take a tour of any wastewater treatment plant and you’ll soon understand the main
objective: to separate the liquids from the solids. Until the mid 90s, most of these solids,
or sludge, used to go into landfills or were dumped in the ocean. But in 1994 the U.S.
Environmental Protection Agency started a program to promote the use of sludge on farm
fields as fertilizer. The EPA thought this was the perfect solution… turning waste into a
useful product.
But scientists have found something which could turn the EPA program on its head.
Rolf Halden is an assistant professor at the Johns Hopkins Center for Water
and Health. He says sludge contains most of the chemicals we use:
“If you look at municipal sludge, it really is a matrix that reflects the chemical footprint
of our society.”
Halden’s focused on one chemical he’s found in sludge called Triclosan – and
there’s a lot of it out there. It’s in antibacterial soaps, and can even be in our toothpastes,
deodorants, and shampoos. Until recently, most if it was thought to break down. Now,
Halden says they found something different:
“In the work that we have done at Johns Hopkins, we have demonstrated for example that
Triclosan when it enters a wastewater treatment plant is not effectively being degraded
and half of the mass is left over.”
Halden and his colleagues found this leftover mass in sludge. And since half the sludge
produced each year in the US goes to fertilize farm fields, Halden says we might want to
think about our food supply:
“We really create a pipeline of contaminants that are first discharged into the water and
then accumulated in sludge and then applied in agriculture which opens a pathway for the
contamination of the food supply and the further distribution of these chemicals in the
environment.”
At this point, scientists are still studying levels of this chemical. They haven’t even
begun to understand Triclosan’s effects in agriculture. But there’s something they do
know about it.
Researchers found Triclosan can mimic a thyroid hormone in the North American
bullfrog and disrupt its growth. When its tadpoles were exposed to low levels of
this chemical for a short amount of time, their growth into a juvenile frog was impaired.
But this doesn’t sound like that big of a deal… the frog doesn’t die, it just doesn’t grow
properly, right? Keep in mind that this study tracked exposure to Triclosan over four
hours. Halden says by spreading wastewater sludge in agriculture, we could be exposing
wildlife to chemicals like Triclosan for their entire lives.
“When these chemicals are transported into the environment with the agricultural
fertilizer, which is the municipal sludge, then they sit there for in the soil, not only for
seconds but for days and weeks and for months and to even years and in some situations
in sediments, in aquatic sediments, they can sit there for decades and this implies that
organisms are, for their lifespan, exposed to very high levels of these contaminants.
What the outcome of that is really not fully understood right now and requires more research.”
The U.S. Geological Survey has also been looking for chemicals in sludge – or biosolids –
and they’ve found steroids, antihistamines, and antidepressants. Ed Furlong, a research chemist
with the USGS in Denver, Colorado, says they are now studying how these chemicals react in agricultural
fields:
“We’ve identified that many of the compounds are consistently present in biosolids from
across the country. We’re now trying to understand what happens after those biosolids
are applied to the soil.”
The USGS is not the only agency looking at this issue. The Environmental Protection Agency has been conducting its own survey of chemicals like Triclosan in sludge. They say the results of the survey won’t be released until next
summer. Then comes the complicated process of deciding what to do with the survey
results. A decision about whether to stop using sludge with hormone disrupting
chemicals to fertilize farm fields could be years away.
For the Environment Report, I’m Kinna Ohman.