A new, three-year study on the common and increasingly controversial practice of spreading treated sewage sludge on farm fields in Pennsylvania concludes the method does not pose a health risk to humans or animals.
Twenty farm fields --including two in Lancaster County --that receive long-term applications of sludge, or biosolids, did show a slight buildup of heavy metals. But the increased concentrations were well below federal limits, the study found. Moreover, there was no evidence that crops grown on the sludge fields absorbed the metals, according to the study that Dr. Richard Stehouwer, a Penn State crop and soil sciences professor, did for the state Department of Environmental Protection.
"Since no difference in the quality of crop tissue grown on treated fields or control fields was found, there was no indication that agronomic use of biosolids has increased the risk of excess amounts of trace elements or nutrients entering the food chain," the study concludes.
Stehouwer, who had suggested the study to the DEP, said he endorses recycling of biosolids on land. "Ag utilization, or re-use of these materials, is what we should be aiming for," he said in an interview. Stehouwer said his findings indicate the sludge-spreading limits and tracking system in place by state and federal regulators is working. DEP officials said Thursday they would not comment on the study because it is undergoing an internal review before being released publicly.
However, Stehouwer stressed that his study did not attempt to deal with all health issues related to the sludge controversy. His study dealt with soil and crop quality and did not tackle the issue of harmful pathogens in sludge. The presence of bacteria, viruses and certain intestinal parasites has emerged as one of the biggest concerns among the public.
The National Academy of Sciences, at the request of the U.S. Environmental Protection Agency, is currently assessing the sludge issue and whether there are any risks from chemical pollutants and pathogens in sludge.
Citizens groups claim a young Berks County boy died in 1999 and a Clearfield County boy in 1994 after contracting a virus from sludge fields. State agencies have maintained the deaths were unrelated to the exposure to sludge.
Biosolids are treated, nutrient-rich organic materials that remain after wastewater at sewage plants is treated. In Pennsylvania, most biosolids are spread for free on farmers' fields as fertilizer, or used to reclaim strip mines. Some sludge is burned in incinerators or landfilled. Some 119 farms in Lancaster County were permitted to receive biosolids in 2000, up from 86 in 1996.
Those opposed to sludge application on land say it contains a witch's brew of toxic metals, chemicals and viruses from such sources as industries and hospitals.
In his study for the DEP, Stehouwer and assistants tested the soil and crops of a field spread with biosolids over three years, and compared it to the soil on untreated fields on the same farms. Eighteen of the farms received biosolids from municipal sewage plants. Two received the sludge from septic-tank-cleaning companies. Most of the farms in the study are in southcentral Pennsylvania because the region has the most widespread use of sludge spreading. One of the Lancaster County farms used in the study was a dairy operation near Wakefield; the other a grain farm near Reinholds. On each of the 20 farms, the soil of treated fields showed higher concentrations of mercury, copper, chromium, molybdenum, manganese, lead and zinc than found on the untreated, control fields. All these elements are regulated by authorities. "The measured differences were too small to be associated with significant risk to crops, humans or animals," the study found. In addition, corn, soybean, hay and sorghum crops were analyzed for buildup of metals. In most cases, not even traces of metals could be detected in the crops. Nor was there any difference in the yields of crops on fields using sludge and those that don't, the study found. While not finding any health concerns, the study did find higher buildups of potentially water-polluting nitrates and phosphorus in fields that receive sludge. Applying more nitrogen and phosphorus than crops can absorb increases the chances that the nutrients will run off into nearby streams or leach into groundwater.
"The results do indicate a need to investigate methods for improved nitrogen management to decrease any potential for off-season nitrate leaching," the study found. "One simple management technique would be to plant a catch crop such as rye to take up any excess nitrates."