Biosolids are the sludge generated by the treatment of sewage at wastewater treatment plants (WWTPs). WWTPs produce a variety of biosolids products for agricultural, landscape, and home use. Recent studies have shown household chemicals in these biosolids
. Depicted in the diagram is an activated sludge tank at a wastewater treatment plant (upper left) and a holding area for biosolids (lower right). (The two photos are not from the same facility.)
A no-till soybean field near an urban area in Iowa, where biosolids were recently applied. Biosolids are produced from the sludge that results from the treatment of sewage at wastewater treatment plants. This field is the site of an experiment to see if earthworms in the field accumulate emerging contaminants, such as household chemicals and drugs, that scientists have found in biosolids. Soybeans in this field were starting to emerge at the time of this photo. Photo Credit: Dana W. Kolpin, USGS
Biosolids from a local wastewater treatment plant were loaded onto trucks for transport to the field. A team of USGS scientists and their colleagues collected samples of biosolids for analysis from freshly exposed surfaces created by the machinery used to load the biosolids onto trucks.
Biosolids were transferred from the dump truck to the spreader prior to being applied to the test field. The application of biosolids on cropland may result in pathways for emerging contaminant uptake by soil fauna (earthworms and other organisms). Photo credit: Dana W. Kolpin, USGS.
Biosolids being spread on the test field to see if earthworms are bioaccumulating emerging contaminants. Prior to this experiment, biosolids had never been applied to this field.
USGS scientists collected samples of soil and worms 31 and 156 days (early growing season and late growing season) after application of the biosolids to the test field (the grayish clumps in the photo are biosolid material). To collect the environmental samples, a 40-centimeter diameter circle was first drawn on the soil surface.
The 40-centimeter (cm) diameter block of soil was then removed from the test field by digging to a depth of about 25 cm within the drawn circle.
Sampling was also conducted using the same protocols at the end of the growing season. The soybean plants in the field are ready for harvest, and are starting to lose their leaves as can be seen by the many brown colored leaves.
The soil was then removed from the 40-cm diameter circle and placed on a clean tarp.
The soil was then carefully sorted to locate all earthworms that were residing in the 40-cm diameter circle.
An example of earthworms found during the sifting process. Because earthworms continuously ingest soils, they could possibly serve as sentinel species that would be indicative of the biological uptake of emerging contaminants. The scientist is wearing gloves to prevent potential contamination of the sample by emerging contaminants that may be on the scientist's hands. Many emerging contaminants being studied are in commonly used products, and thus additional precautions are required to prevent inadvertent sample contamination.
A tarp containing the soil from the 40-cm diameter circle that USGS scientists sifted for worms during sample collection at the end of the growing season. This soil had a high sand content and was very friable (clumps of soil were easily broken). Mature pods of soybeans can be seen on either side of the soil sample.
All earthworms located during the sifting process were removed from the soil and were placed in a shipping container (container on left) with loosely packed native soil. The container had holes to allow air to enter the container. A portion of the soil was collected in a separate container (glass container on right) to generate a composite soil sample from the test field. The composited soil was split into a set of sampling jars for chemical analysis of a broad suite of emerging contaminants.
The earthworms collected from the soil were counted, placed into a storage container containing native soil, and shipped to a laboratory. At the laboratory, the worms were cleaned using cool deionized water and allowed to depurate on wet filter paper for 24 hours to assure that any emerging contaminants detected in the earthworms originated from tissue and not ingested soil. After depuration, the earthworms were cleaned with cool deionized water and frozen for later extraction emerging contaminants and chemical analysis.
A scientist from Eastern Washington University (now with Colorado State University-Pueblo) preparing samples of biosolids for extraction using accelerated solvent extraction. Such samples were analyzed for a broad suite of emerging contaminants.