South-central Arkansas (AR) is home to major manufacturing facilities for brominated flame retardant chemicals (BFRs) in the U.S. Unintended release during production may have caused accumulation of the BFRs in the local environment. In this work, sediment cores were collected from six water bodies in AR, including three located close to the BFR manufacturing facilities in El Dorado and Magnolia, to investigate past and recent deposition histories. A total of 49 polybromodiphenyl ethers (PBDEs) and decabromodiphenyl ethane (DBDPE) were detected, with concentrations as high as 57000 and 2400 ng/g dry weight for decabromodiphenyl ether (BDE209) and DBDPE, respectively. Log-log regression of BDE209 and DBDPE surface concentrations versus distance to known BFR manufacturing facilities fit the Gaussian Plume Dispersion model, and showed that, if the distance is shortened by half, concentrations of BDE209 and DBDPE would increase by 5-fold. The spatial distribution and temporal trend of the contamination indicate that the manufacturing of PBDEs and DBDPE is the primary source for these compounds in the environment of southern Arkansas. Interestingly, the occurrence of debromination of PBDEs in the sediments of a previously used wastewater sludge retention pond in Magnolia is indicated by the presence of congeners that had not been detected in any commercial PBDE mixtures and by increased fractions of lower brominated congeners relative to higher brominated congeners. Two unknown brominated compounds were detected in the sediments, and identified as nonabromodiphenyl ethanes.

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A previously generated data set for polybrominated diphenyl ethers (PBDEs) in dated sediment cores of West Lake of El Dorado (AED), Calion Lake (ACL), and the lagoon of Magnolia Wastewater Treatment Facility (AMW) from Southern Arkansas is examined by a weighted chemical mass balance (CMB) model and positive matrix factorization (PMF) in order to quantify PBDE sources and debromination. DNA extraction and pyrosequencing were done on several core sections in order to investigate microbial debromination. CMB and PMF analyses indicate that deca technical mixtures are the dominant PBDE input (>99% in mole fraction in AED and ACL, and 94.7% in AMW). Minor contributions of penta and octa technical mixtures were found in all three water bodies (<1% in AED and ACL; and 1.1% and 4.1% in AMW, respectively). Results suggest that debromination takes place in all three lakes, but is more intense in AMW. In-situ microbial debromination was supported by the microorganism analysis. The PMF results are validated by PBDE manufacturing records, and the operating history of AMW. Despite the high PBDE concentrations in these sediments near former manufacturing facilities, the extent of debromination is limited, possibly due to sorption to natural organic matter of the sediment.

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Field application of livestock manure introduces animal hormones and veterinary antibiotics into the environment. Colloids present in manure may potentially intensify the environmental risk of groundwater pollution by colloid-facilitated contaminant transport. The transport behavior of the veterinary antibiotic florfenicol in saturated homogeneously packed soil columns has been investigated in both the presence and absence of manure colloids. Results show that facilitated transport of florfenicol is significant in the presence of manure colloids. Multiple chemical and physical processes caused by the presence of manure colloids were considered to contribute to facilitated transport. Florfenicol breakthrough curves (BTCs) were fit well by two models. The two-site nonequilibrium adsorption contaminant transport model suggested the mechanisms for facilitated florfenicol transport are as follows: manure colloids decrease the sorption capacity of florfenicol to soil, enhance the instantaneous equilibrium adsorption, and suppress the time-dependent kinetic adsorption processes. The colloid-facilitated model further evaluated the partition coefficient of florfenicol to colloids and indicated that cotransport has little contribution. A stepwise inverse model fitting approach resulted in robust parameter estimation. The adoption of the nonlinear Freundlich adsorption equation in the two-site nonequilibrium model significantly increased the fit of the model to the breakthrough curves.