Bioassays Applied to Biosolids
Bioassays are tests that use common plants and animals to assess the potential toxicity of a material. Bioassays are commonly used in water quality testing, for example. And yeast bioassays are used to assess the potential for chemicals to affect the hormone systems in humans and other organisms.
Applying bioassays to biosolids is not new. For example, several large-scale biosolids land reclamation projects since the 1970s have included testing of plants and animals living on the reclaimed sites after biosolids were applied.
Today, there is increasing interest in research using bioassays to assess the overall impacts of the most common uses of biosolids: in agricultural settings. With people expressing concerns about tens of thousands of synthetic chemicals in use, many of which might be in biosolids (in parts per million or billion or less), the challenge of testing every chemical, one-by-one, seems more overwhelming than ever. Yes, research on the highest production chemicals and those considered of greatest potential toxicity does provide insights into potential impacts from microconstituents. But answering questions about the possible synergistic, combined effects of the mixture of trace chemicals found in biosolids requires something different: bioassays.
Using a variety of plants and soil and aquatic organisms to determine the overall impacts of biosolids use on soils can provide a relatively time-efficient and cost-effective sense of the potential for positive and negative impacts. If this kind of bioassay screening finds significant overall negative impacts, then scientists can follow up with traditional analyses of individual chemicals, to isolate the cause of the impact.
To date, bioassays applied to several different biosolids products have not found significant net negative impacts. In fact, the opposite is true: biosolids stimulate soil microbial activity and plant growth by adding nutrients and organic matter.
A Biosolids-Bioassays Workshop - May, 2011
At the Water Environment Federation annual Residuals & Biosolids Conference in Sacramento, CA in May, 2011, a workshop was offered regarding using bioassays to evaluate potential impacts of biosolids.
The workshop presenters from the U. S., Canada, and Germany came to agreement that bioassays can provide a cost- and time-efficient screen that can then inform and direct further chemical-by-chemical research, as needed. “Ask the bugs and bunnies, first,” Dr. Linda McCarthy of Ryerson Univ. emphasized; then, if impacts are noted, further research is warranted.
McCarthy, whose past research has applied bioassays for understanding anthropogenic impacts on the Great Lakes water environment, conducted bioassays of several land-applied Ontario biosolids in the late 2000s, using a wide variety of macroscopic soil and aquatic animals, as well as plants. Her analysis is far more comprehensive than seeing whether Daphnia die or not: her team looks for impacts such as stress indicators in Daphnia in biosolids runoff water, changes in behavior (soil organisms avoiding biosolids soil), impacts in any of the life cycle of plants (the bioassays follow native and crop plant development from seed germination through plant growth to seed production and the viability of the next generation of seed), and reproduction (e.g. of earthworms living in biosolids-amended soil). For the biosolids tested, McCarthy’s team found no significant differences between the biosolids-amended tests and controls.
Tom Young of the Univ. of CA at Davis has been using microbial bioassays to evaluate potential impacts from microconstituents in biosolids, such as the antibiotics triclosan (TCS) and triclocarban (TCC). Even using spiked biosolids-amended-soil samples, his team found only a minimal reduction in the activity of some soil bacteria, while there was a far more dramatic increase in overall numbers (the enrichment effect caused by the biosolids nutrients and organic matter), resulting in a significant net increase in microbial respiration and activity. (Although I missed it, I heard that in another presentation he made later in the conference, he reported on a study of the levels of these antimicrobials in people’s urine immediately following showering using soaps containing them: absorption through the skin led to levels in their urine peaking several hours later at levels more significant than those in biosolids. Also, note that FDA does not believe, as of May 2011, that changes in use of TCS is warranted, but they are evaluating the latest information and may change their stance on the matter.))
Anja Coors’ ongoing research, also in Ontario, uses a wide variety of nematodes and enchytraeids (potworms) to evaluate community population changes after biosolids land application. As with plants, these soil organisms go through phases of succession, from a “pioneer” community to longer-lasting mature communities; a “maturity index” is one tool used to assess the impact of the land application of biosolids. As with the microbial community, biosolids addition stimulates activity and leads to increased populations; Coors has found this enrichment effect lasts about two years in the nematode populations. The land application and tilling of the soil stimulates more pioneering species, resulting in a lower maturity of the nematode populations, which rebounds some, but not all the way, in two years. Biosolids had a greater effect in this way than did the control. The benefits to these soil organisms was also demonstrated by their significantly increased feeding behavior. On the other hand, after two years, the longer-living, nematode “persister” populations did not recover to the same levels as in the control soils, which Coors is watching further. She is continuing further sampling and will be publishing initial results this year.
The workshop presenters kindly agreed to share their presentations; download them below.
Presentations from the Workshop "Applying Bioassays to Biosolids"
May 22, 2011, Sacramento, CA
Workshop Welcome and Introduction to the Topic (PDF, 3 pp.) - Ned Beecher, NEBRA and Jody Slagle, City of Austin, TX
"The Evolution to the Bioassay" (1.1 MB) - Michael Payne, Black Lake Environmental and OMAFRA, retired 2011
"Why Not Bioassays for Biosolids?" (3.2 MB) - Robert K. Bastian, U. S. EPA
"Principles of Bioassays" (2.8 MB) - Lynda McCarthy, Ryerson University
"Bioavailability as a Tool for Risk Assessment" (1.7 MB) - Sally Brown, University of Washington
"Bioassays of Biosolids Land Application in Ontario" (1.8 MB) - Lynda McCarthy, Ryerson University
"Bioassays of a Biosolids Land Application Site in Ontario Using Structural and Functional Endpoints of Soil Organisms" (1 MB) - Anja Coors, ECT Oekotoxikologie GmbH, Germany