Progress 08/22/16 to 09/30/19
Outputs
Target Audience:Agricultural producers have a choice of whether to utilize municipal biosolids (a stabilized by-product of wastewater treatment plants) as a crop amendment. The land application of biosolids for crop production is an attractive disposal option for the public at large, when considering cost. However, many factors affect whether this sometimes controversial product is used for crop production. First and foremost, is a demonstration that biosolids provide plant nutrients, particularly nitrogen and phosphorus, that increase plant yield. The crop production increase must offset the cost (if any) of acquisition and land application of biosolids. Beyond this simple initial consideration, agricultural producers, and the general public, are justly concerned about the potential for plant uptake of heavy metals and trace organic chemicals (TOrCs) that are present in biosolids (for example, copper, zinc, pharmaceuticals, and personal care products). Plant uptake of heavy metals and trace organic chemicals from biosolids is not well understood, but obviously affects food safety.This project assesses this concerns with controlled studies that define the effects of biosolids soil amendment on fescue and corn yield, and also quantifies plant uptake of heavy metals and trace organic chemicals. The ultimate goal is to define the practical effect of using biosolids for crop production (increased yield) and to quantify and place perspective on the potential for plant uptake of heavy metals and toxic organic chemicals from biosolids form a food safety perspective. Information gathered using this work will help producers determine whether their crops should be produced with biosolids, and whether the public as a whole should condone this practice as another technical to make our society more sustainable. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Project data wereused forin-servicetraining for University of Extension County Extension professionals and agricultural producers during 2017-2019. How have the results been disseminated to communities of interest?Project data were presented to water quality professionals during the 2018 Tennessee Water Resource Symposium. Publications from the project are in preparation for release during2020. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
This project was designed to assess the safety and sustainability of land applying solids recovered by the wastewater treatment plants (WWTPs). We conducted experiments to assess the risk associated with plant uptake of biosolids components, including metals such as arsenic and cadmium, as well as Trace Organic Chemicals (TOrCs) including drug residues. Our experiments employed crops commonly fertilized with biosolids, namely fescue grass and corn. We gathered practical data farmers need to manage land application, namely the plant availability of nitrogen (37)%. Our experiments confirmed that the metals content in soil amended with the tested biosolids were below regulatory levels even at biosolids application rates much higher than expected during crop production. This contributes valuable knowledge for the public and farmers to consider and confirms that EPA's regulatory requirement over the last several decades to pre-treat industrial wastewater prior to discharging to municipal wastewater has significantly lowered toxic metals concentrations in biosolids. These data will help stimulate change by encouraging farmers to recycle biosolids sustainably through land application, replacing a fear of a soil buildup of toxic metals with the knowledge that biosolids can serve as an important plant micronutrient source. TOrCs were detectable in soil amended with biosolids and within fescue roots. However, the measured concentrations were extremely low and only occurred at impractically high biosolids application rates. Further, these chemicals were below detection limits in the forage and corn grain. This is an important finding and indicates it is unlikely that TOrCs are transported to the edible above ground portion of crops in quantities that represent a food safely risk. Our findings benefit farmers by providing data to land apply biosolids efficiently and help answer public concern about the fate of heavy metals and TOrCs during crop production using land applied biosolids. Our research directly addressed the goal of the project to evaluate the plant bioavailability of nutrients, metals, and trace organics. We completed a three-year plot study and on-going supplemental plot studies to evaluate the yield and forage quality of tall fescue-dominated grass stands to Nashville Metro Exceptional Quality (EQ) biosolids (0.75, 1, 1.5, and 3 tons/acre). Results were evaluated with control treatments, namely a negative control with no fertilizer, a positive control using chemical fertilizer (60 lbs/acre of nitrogen in the spring and fall with supplemental phosphate and potassium per soil tests), and a second positive control using chemical fertilizer applied using "producer practice" (300 lbs of a 19-19-19 blended fertilizer in the spring only). Findings indicated that moderate (1.5 tons EQ biosolids/acre, 2 tons broiler litter/acre) and high (3 tons EQ biosolids/acre, 4 tons broiler litter/acre) application rates of spring applied biosolids increase yield and forage quality (e.g. crude protein content, ANOVA-Tukey HSD analysis; p<0.05). Spring nitrogen availability was 32±7%. Fall hay yield and forage quality were typically similar for all treatments, so carryover and release of nitrogen from the spring applied biosolids was negligible. The study clearly indicated that biosolids provide soils with plant available micronutrients because spring forage concentrations of both copper and zinc increased as the biosolids application rate increased. This is beneficial because beef cattle that consume fescue forages are prone to copper deficiencies. A greenhouse study was also conducted using potted corn and fescue fertilized with a Class B biosolids to evaluate plant yield as well as uptake of heavy metals and TORCs across a range of biosolids amendment rates: 0%-soil only control, 1%, 5%, 10%, and 50% dry matter). The effect of the biosolids amendment was to increase forage yields over those obtained with chemical fertilizers, with diminishing yield when the biosolids amendment rate increased beyond 10%, a high rate only used for land recovery and not crop production. Biosolids addition clearly improved corn grain and total plant dry mass yields versus the soil only control. Corn and fescue mortality observed with the 50% biosolids treatment appeared to be related to the high-water retention caused by the high organic matter that resulted seed and plant rot. For both fescue and corn plots, soil nitrogen and carbon concentrations increased with increasing biosolids rates, indicating improvements in soil tilth and soil fertility are likely when soil is regularly fertilized with biosolids. For the greenhouse study, growth media concentrations of all heavy metals were below Exceptional Quality limits set by EPA, even when soils were amended with 50% (dry basis) biosolids. Plant uptake of magnesium, manganese, copper and zinc was observed for fescue forage and corn stover but not corn grain; no significant uptake of cadmium, arsenic, or chromium were observed even at very high amendment rates. Plant magnesium, manganese, and copper and zinc concentrations remained well below plant toxicity thresholds. As with the earlier fescue plot study with EQ biosolids, the increase in copper concentrations observed during the greenhouse study with Class B biosolids would be expected to improve a known problem with beef cattle copper deficiency observed in Tennessee. A Kruskal-Walis test was used to assess two study hypotheses: Hypothesis 1 - TOrC concentrations were below the detection limit in roots of plants grown in biosolids amended soil and Hypothesis 2 - TOrCs did not bio-accumulate in plant tissue irrespective of the biosolids amendment rate (Table 40). Both of these hypotheses were easily rejected for many TOrC compounds, including a subset that displayed median plant tissue concentrations above the EPA method limit for quantitation (ML): caffeine, carbamazepine, cotinine, dehydronifedipine, diphenhydramine, fluoxetine, miconazole, ofloxacin, sulfanilamide, and trimethoprim in Group 1; ATC, EACTC, and tetracycline in Group 2; and ibuprofen in Group 3 (Figure 24). While uptake of these TOrCs was measurable in fescue roots, the concentrations observed were extremely low and occurred only at a very high soil biosolids amendment rate (10% dry matter: 5-10 times higher than agricultural producers would normally be expected to use). Further, uptake to fescue forage and corn grain was not observed for any of the TOrCs. The current study contributes unique knowledge for the stated project goal, namely by including an experimental design that included a broad range of un-spiked biosolids application rates to the most relevant crops, namely pasture/hay grass and corn, which receive much of the US biosolids that are land applied. The study collected data that include a TOrC plant uptake control, namely copper and zinc. Further, a very high application rate was studied, 10% dry matter, which offers insight into the potential effects of very long-term application of biosolids to agricultural soils. The data collected clearly indicate that plant uptake of biosolids components occurs (e.g. of copper and zinc), and that the uptake of TOrCs to the edible parts of the plants studied are not measurable. This new knowledge is currently being submitted for publication in a professional journal.
Publications
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Progress 10/01/16 to 09/30/17
Outputs
Target Audience:The primary target audience during the past reporting period was the wastewater treatment plant utility districts that generate biosolids for land application. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?Corn grain and fescue leaf tissue from plants grown with varying amendment rates of biosolids will be subject to Trace Organic Chemical (TOrC) analysis during the next reporting period.
Impacts
What was accomplished under these goals?
Agricultural producers have a choice of whether to utilize biosolids, a stabilized residual of municipal wastewater treatment, for crop production benefit. A long-term concern of agricultural producers is whether heavy metals within biosolids buildup in the soil or are transported into crop tissue. In fact, biosolids are highly regulated by the USEPA, particularly with respect to their heavy metal concentrations, and these regulations are designed to protect both the agricultural producer and public. Research during the past year evaluated whether crop heavy metal uptake occurred from a biosolids meeting EPA's most stringent risk based regulatory thresholds for heavy metal concentrations. An Objective of this project is to "Evaluate plant uptake and ecological effects of potentially toxic trace elements and TOrCs from soils amended with residuals and reclaimed wastewater." During the reporting period corn grain and stover, produced by plants grown with varying amendments rates of a municipal biosolids (1, 5, 10, and 50% by dry mass), were ground and extracted for heavy metals analsysis. Data generated were for two years of in-season greenhouse experiments for grain and one season for corn stover, specifically concentrations of arsenic, cadmium, calcium, chromium, copper, magnesium, manganese, lead, and zinc. Clear evidence of plant uptake into stover occurred only for copper, magnesium, manganese, and zinc, but uptake was consistent among in these trace elements, varying with increasing biosolids amendment rates and/or plant vigor. Fodder copper concentrations increased from approximately 45 ppm in the soil only control, to approximately 90 ppm in soil amended with 5% biosolids by dry mass, but was reduced at the 10% amendment rate, which negatively affected plant vigor, to 75 ppm. A similar tread was observed for magnesium, manganese, and zinc, respectively, which ranged from 8, 0.6, and 0.2 ppm up to 50, 1.2, and 0.4 ppm, respectively. Concentrations of copper and manganese were much lower in the corn grain, at a range of 12-20 ppm and 10-17 ppm, respectively. However, concentrations of manganese were much higher in the corn grain than fodder, ranging from approximately 30 ppm in the soil only control, to as high as 80 ppm at the 5 and 10% biosolids amendment rates. Zinc displayed a clear trend in corn grain accumulation as a function of the biosolids amendment rate, increasing from approximately 0.2 ppm in the soil only control, up to 0.45 ppm in the 5 and 10% biosolids amendment rates. The results are preliminary, but do indicate that uptake of metals from land applied biosolids does occur from those biosolids meeting EPA's most stringent risk based regulatory thresholds. However, the concentration increases in the corn grain and fodder in these experiments were small, even for very large biosolids application rates that likely cannot be agronomically justified.
Publications
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