Sorption of two classes of emerging contaminants by dissolved organic carbon from diverse sources

In the past decade, diverse organic chemicals from industrial, agricultural, and commercial products have been identified as emerging contaminants (ECs) in the environment. Land disposal of biosolids from municipal wastewater treatment plants (WWTPs) and manure from confined animal feeding operations (CAFOs) is an exposure route for certain ECs. Among these are fluorotelomer alcohols (FTOHs) and amphoteric antimicrobials. Recent studies on these EC classes have reported a high affinity for dissolved organic carbon (DOC), raising concerns that DOC from biosolids, animal wastes, or soils may facilitate their global distribution by DOC-enhanced transport. However, direct measurements of DOC-water partition coefficients (Kdoc) with environmentally-relevant DOC materials are lacking. Therefore, K doc values were quantified for select FTOHs and the amphoteric antimicrobial ciprofloxacin (CIP) using standard humic materials, WWTP biosolids and effluent, beef lagoon effluent, and soils to evaluate the mechanisms and potential magnitude of facilitated transport by environmentally-relevant DOC. Measured log Kdoc values for a 10-carbon FTOH (8:2 FTOH) ranged from 2.00–3.97, which are 1–2 log units lower than estimated values, and slightly lower than measured OC-normalized sorption to soils. These Kdoc values result in potential increases in mobility of 8:2 FTOH of 1% to 50%. For CIP, sorption isotherms with standard DOC materials were nonlinear and well the Langmuir sorption model. Decreases in sorption with increasing pH are attributable to reductions in the fraction of the cationic CIP species, exemplifying the importance of sorption by cation exchange. CIP sorption by digested biosolids DOC was also non-linear but did not exhibit pH-dependence, suggesting the occurrence of additional unidentified binding processes. At CIP concentrations reported in biosolids (∼ 2 mg/L) and the DOC concentrations associated with the biosolids in this study (40 mg OC/L), the measured log K doc of ∼ 4 could potentially increase CIP mobility by ∼ 15%. Interaction of ECs and DOC with soil must also be considered when assessing mobility of ECs in the environment; however, the extent of FTOH and CIP interactions with environmentally-relevant DOC exemplified here warrants that DOC-facilitated transport should be included in assessments of the global distribution of these EC classes

Soil Microbial Community Responses to Additions of Organic Carbon Substrates and Heavy Metals (Pb and Cr)

Microcosm experiments were conducted with soils contaminated with heavy metals (Pb and Cr) and aromatic hydrocarbons to determine the effects of each upon microbial community structure and function. Organic substrates were added as a driving force for change in the microbial community. Glucose represented an energy source used by a broad variety of bacteria, whereas fewer soil species were expected to use xylene. The metal amendments were chosen to inhibit the acute rate of organic mineralization by either 50% or 90%, and lower mineralization rates persisted over the entire 31-day incubation period. Significant biomass increases were abolished when metals were added in addition to organic carbon. The addition of organic carbon alone had the most significant impact on community composition and led to the proliferation of a few dominant phylotypes, as detected by PCR-denaturing gradient gel electrophoresis of bacterial 16S rRNA genes. However, the community-wide effects of heavy metal addition differed between the two carbon sources. For glucose, either Pb or Cr produced large changes and replacement with new phylotypes. In contrast, many phylotypes selected by xylene treatment were retained when either metal was added. Members of the Actinomycetales were very prevalent in microcosms with xylene and Cr(VI); gene copy numbers of biphenyl dioxygenase and phenol hydroxylase (but not other oxygenases) were elevated in these microcosms, as determined by real-time PCR. Much lower metal concentrations were needed to inhibit the catabolism of xylene than of glucose. Cr(VI) appeared to be reduced during the 31-day incubations, but in the case of glucose there was substantial microbial activity when much of the Cr(VI) remained. In the case of xylene, this was less clear

Probing the Primary Mechanisms Affecting the Environmental Distribution of Estrogen and Androgen Isomers

Land application of animal manure has been identified as a source of natural and synthetic hormone contaminants that are frequently detected down-gradient of agricultural operations. Much research on the environmental fate of hormones has focused on the structural isomers most biologically active in mammals, e.g., the 17 beta-isomers of the estrogen estradiol (E2) and the synthetic androgen trenbolone (TB). However, recent work has shown that the alpha- and beta-isomers of E2 and TB can cause comparable effects on certain aquatic species. To improve our understanding and ability to predict isomer-specific interactions with environmental sorbents, we measured the association (K-DOC) of the alpha- and beta-isomers of E2 and TB as well as their primary metabolites (estrone and trendione) with two commercial dissolved organic carbon (DOC) sources by measuring both free and DOC-bound hormone concentrations. We also measured solvent-water partition coefficients partitioning (K-SW) for the same hormones using hexane, toluene, and octanol. Log K-DOC log.K-OC (OC-normalized sorption by soils), and K-OW values are all greater for the beta-isomer except between the E2 isomers. Theoretical descriptors reflecting electronic character and solute-solvent interactions were calculated to elucidate isomer-specific behavior. Trends for log K-OW and log K-DOC among hormones as well as between isomers are explained reasonably well by computed electrostatic potential and H-bonding parameters.Land application of animal manure has been identified as a source of natural and synthetic hormone contaminants that are frequently detected down-gradient of agricultural operations. Much research on the environmental fate of hormones has focused on the structural isomers most biologically active in mammals, e.g., the 17 beta-isomers of the estrogen estradiol (E2) and the synthetic androgen trenbolone (TB). However, recent work has shown that the alpha- and beta-isomers of E2 and TB can cause comparable effects on certain aquatic species. To improve our understanding and ability to predict isomer-specific interactions with environmental sorbents, we measured the association (K(DOC)) of the alpha- and beta-isomers of E2 and TB as well as their primary metabolites (estrone and trendione) with two commercial dissolved organic carbon (DOC) sources by measuring both free and DOC-bound hormone concentrations. We also measured solvent-water partition coefficients partitioning (K(SW)) for the same hormones using hexane, toluene, and octanol. Log K(DOC) log.K(OC) (OC-normalized sorption by soils), and K(OW) values are all greater for the beta-isomer except between the E2 isomers. Theoretical descriptors reflecting electronic character and solute-solvent interactions were calculated to elucidate isomer-specific behavior. Trends for log K(OW) and log K(DOC) among hormones as well as between isomers are explained reasonably well by computed electrostatic potential and H-bonding parameters