ASSESSING THE FATE AND BIOAVAILABILITY OF HYDROPHOBIC ORGANIC POLLUTANTS IN AGRICULTURAL SOILS

Abstract

Persistent organic pollutants have been the cause of concern for many decades; however, little information is available about their environmental fate. One goal of this work was to assess whether land application of biosolids represents a source of persistent organic pollutants to agricultural soils. To address this goal, we developed a methodology to quantify low levels of the flame retardants polybrominated diphenyl ethers (PBDEs) in biosolids and soils and conducted field studies to determine the fate and persistence of PBDEs upon the land application of biosolids. We found that biosolids can take up to one year to completely incorporate into the soil matrix after application and biosolids-bound chemicals are released during this time. PBDEs profiles in soils that receive biosolids applications are similar to PBDEs profiles in biosolids and both reflect commercial formulations of these flame retardants, indicating that biosolids are a source of these chemicals to soil. Residence time of these chemicals was reported for the first time and it was estimated at 16 yr. for the sum of BDE-47 and BDE-99. An abiotic methodology to assess bioavailability of aged soil residues was developed and results were compared to earthworms. The study illustrated that the polymer-based abiotic methodology can be used to assess the bioavailability of soil-bound hydrophobic organic chemicals to earthworms. Measured soil-polymer equilibrium concentration ratios of organic pollutants correlated strongly with earthworm bioaccumulation factors using the same soils. A laboratory protocol to introduce the concept of fugacity and bioavailability to undergraduate and graduate environmental science and engineering students was developed based on the methodology developed for research. The experiment provided an excellent opportunity for students to become familiar with the laboratory protocols and techniques for quantitative analysis as well as graphical analysis of data. The totality of this work improves knowledge of the fate of two classes of organic pollutants in soils. This work substantially adds information and understanding of chemical behavior to the general environmental engineering field. Although this unique experiment provided original and essential pieces of information, additional research is crucial to address the difficulties involved in assessing the environmental behavior of organic pollutants.