Uptake of pharmaceuticals and personal care products by soybean plants from soils applied with biosolids and irrigated with contaminated water
Wu, C, AL Sponberg, JD Witter, M Fang and KP Czajkowski.
Synopsis by Heather Stapleton and Wendy Hessler.
Environmental Science and Technology, Aug 30, 2010
New research shows that the drugs and contaminants that often contaminant sewage sludge that is used as fertilizer can be taken up by the plants grown in fertilized fields and gardens. Also called ‘biosolids’ these fertilizers are regularly applied to agricultural fields and are sometimes packaged as organic soil fertilizers sold in home improvement stores. The results raise significant public health concerns about use of biosolids on croplands and in gardens used to grow produce for consumption.
Wastewater treatment plants are important in maintaining a healthy environment. Their primary function is to clean dirty water of pathogens, metals, certain nutrients and some pollutants that exit homes and businesses through showers, toilets, laundry machines, dishwashers and other drains.
During treatment, the sewage is separated into liquids and solids. The extent of treatment can vary, but, generally, bacteria help to break down chemicals present in the dirty water. The water can be aerated and disinfected to kill disease-causing pathogens. The cleaner water – now called effluent – is released into the environment, either directly into rivers, oceans and other natural waterbodies or reused to irrigate crops.
Any solids in the sewage are filtered out. The solid materials – called sewage sludge, or “biosolids” – are dried before disposal. But, getting rid of the solids can be expensive. They can be put in a landfill, incinerated or composted for reuse as fertilizers for crops or home garden/lawn use.
Today, most biosolids are land applied to recover nutrients in the solids. Biosolids are currently regulated by the U.S. Evironmental Protection Agency (EPA) for metals and pathogens, but not for organic contaminants, including pharmaceuticals, cleaning product ingredients and persistent chemicals. The EPA requires testing for only nine pollutants, about 1 percent of the hazardous materials that could be found in sewage.
Based on recent studies, some scientists are now questioning whether land application of biosolids may be harmful to the environment and to people’s health. A main concern is the release of these contaminants back to the environment, and possible human exposure to the chemicals in crops grown in biosolid-treated fields. Previous studies have focused mainly on identifying and measuring the organic contaminants in the biosolids and in the fields and soils treated with biosolids. Some research has found the pollutants do not always stay put. They can run off into waterways, soak into groundwater or become airborne and blow away in the wind. Whether the contaminants can get into crops or be passed on to livestock and people who eat them is not known.
What did they do?
A group of U.S. scientists collected biosolids – also called sewage sludge – and wastewater effluent from a local wastewater treatment plant in Oregon, Ohio. The biosolids were mixed with local soil and added to nursery pots sowed with soybean seeds. The plants grew in a greenhouse for up to 110 days. Some plants were also grown in other nursery pots that contained local soil only (i.e. without the biosolids.) Some pots were irrigated with wastewater effluent and some with clean water.
The plants grown with the biosolids in the soil were compared with plants grown in clean soil. They were also compared with the plants irrigated with the wastewater, but grown in clean soil. Samples of soil and plant tissues were collected halfway through the study and at the end of the study. They were analyzed for three different types of pharmaceuticals – carbamazepine(an anticonvulsant), diphenhydramine (a histimine) and fluoxetine (an antidepressant) – and two anti-microbial compounds – triclosan andtriclocarban, which are typically found in anti-bacterial soaps and toothpastes.
The investigators determined whether these chemicals could be taken up by the roots of the soybean plant and transferred to the leaves and other parts of the plant. After harvesting, the concentrations of the chemicals were measured and compared in the roots, stems, leaves and beans.
What did they find?
With the exception of fluoxetine, all of the chemicals accumulated in the plant tissues from exposure to both wastewater and biosolids. The greatest accumulation was observed for carbamazepine, triclosan and tricloarban. Concentrations increased in the plant tissues up to six times the levels present in the biosolid amended soils. Greater accumulation of all chemicals was found in the soybeans exposed to soils treated with biosolids; however, this may be partially due to the naturally higher concentrations of these chemicals in the biosolids versus the wastewater.
The two anti-microbial chemicals triclosan and triclocarban were found to have the highest concentrations in the leaves of the soybean plants relative to the root, suggesting these chemicals had a greater potential to move upward in the plant tissues. This has implications for exposure since most livestock feed upon the leaves and upper part of the plants, as opposed to the roots. In addition, uptake of these chemicals from roots to leaves was greater for the plants exposed to the wastewater, not the biosolids, suggesting differences in remobilization of the chemicals based on route of exposure.
What does it mean?
The research demonstrates that chemical contaminants found in wastewater and sewage sludge may accumulate in plants grown in fields receiving applications of biosolids and/or wastewater effluent. The levels and accumulations varied among the chemicals measured and between the two treatment types.
This was one of the first studies to explore uptake of pharmaceutical compounds in plants grown under greenhouse laboratory conditions. Additionally, this was the first study to explore movement of these chemicals from the roots to the leaves.
The researchers report that the antimicrobial chemicals concentrated in the plants leaves and were measured at the highest levels of the five chemicals analyzed. As the biocides move from soil and wastewater to the leaves, human, wildlife and livestock could be exposed to these drugs.
This leads to a two-fold problem. First, more exposures could cause increased antibiotic resistance. Antibiotic resistance occurs when disease-causing bacteria become resistant to the antibiotics intended to control them. This serious problem is on the rise due to the high use of antimicrobial agents in everyday personal care products and the overuse of antibiotics in health care. Second, both antimicrobials and antibiotic resistance bacteria could be passed from livestock to people.
Previous studies have measured contaminants in biosolids from different areas of the country, and several studies have investigated contaminant residues in soils/fields treated with biosolids over a few years to decades. Many different types of organic pollutants have been found in biosolids and in fields treated with biosolids all over the country, including polychlorinated biphenyls (PCBs), pesticides, dioxins/furans, polycyclic aromatic hydrocarbons (PAHs) and flame retardant chemicals such as polybrominated diphenyl ethers (PBDEs).
Both the application of biosolids as fertilizers and irrigatation with wastewater are popular practices due to the increasing volumes of sewage sludge and wastewater generated and the high costs of disposal. Biosolids are even now applied to forested areas to increase timber production.
Unsuspecting people may be buying the biosolids, sometimes labeled as organic, from their local home improvement store and then using them on vegetable gardens and flower beds. If they can move to leaves, people may be eating contaminants taken up by garden plants and not know it.
Given all this information, the study has some limitiations. The authors used biosolids with a very high water content, which may not represent actual land application practices. They also added more of the chemical contaminants to the biosolids to increase their concentrations, instead of monitoring the chemical levels present in the biosolids and wastewater. This may alter how the chemicals disperse and result in more chemicals available to the roots of the soybean plants in the experiment than would be under real-world applications.
Further research studies should examine uptake of these chemicals in plants grown in biosolids that are not “spiked” with these chemical contaminants.
For the full report, go to: http://dx.doi.org/10.1021/es1011115