Leachability and potential ecotoxic impact of trifluralin-impregnated mulch

The leachability, potential ecotoxicity, and photolysis of trifluralin-impregnated mulch, a popular retail consumer gardening product, were investigated under environmentally realistic conditions. Leachability of trifluralin from impregnated mulch was low (< 1% of total extractable compound) and in the range of reported values for agricultural soils. No trifluralin transformation products were detected in mulch leachate. Yeast-based estrogenicity and androgenicity screens indicated that aqueous trifluralin is not estrogenic but is moderately androgenic at concentrations ~ 1e - 5 M. Impregnated mulch leachate was not hormonally active, even at undiluted concentrations, but it did exert nonspecific toxicity at dilutions of ~ 1:10. Photolysis of trifluralin was investigated in acetonitrile and water and on mulch surfaces. Degradation on mulch surfaces was diffusion-limited; it was ~ 17 times slower than in aqueous solution, but faster than has been reported on kaolinite. An array of trifluralin transformation products was identified, but in no case did they exceed 10% of the parent compound. Using industry-recommended application guidelines, it is estimated that as much as 1400 μg/m² of trifluralin may leach from impregnated mulch upon the first rainfall. However, provided that consumers are aware that such mulch products contain trifluralin and are properly educated about its use, the potential for direct ecotoxic impact is likely to be small.

Stability of cocaine and its metabolites in municipal wastewater--the case for using metabolite consolidation to monitor cocaine utilization

Transformations of cocaine and eleven of its metabolites were investigated in untreated municipal sewage at pH ≈ 7 and 9, 23, and 31 °C. Results indicated that hydrolysis-possibly bacterially mediated-was the principal transformation pathway. Residues possessing alkyl esters were particularly susceptible to hydrolysis, with pseudo-first-order rate constants varying from 0.54 to 1.7 day(-1) at 23 °C. Metabolites lacking esters or possessing only a benzoyl ester appeared stable. Residues lacking alkyl esters did accumulate through hydrolysis of precursors, however. As noted previously, this may positively bias cocaine utilization estimates based on benzoylecgonine alone. Reported variability in metabolic excretion was used in conjunction with transformation data to evaluate different approaches for estimating cocaine loading. Results indicate that estimates derived from measurands that capture all major cocaine metabolites, such as COCtot (the sum of all measurable metabolites) and EChyd (the sum of all metabolites that can be hydrolyzed to ecgonine), may reduce uncertainty arising from variability in metabolite transformation and excretion, possibly to ≈ 10 % RSD. This is more than a two-fold reduction relative to estimates derived from benzoylecgonine (>26 % RSD), and roughly equivalent to reported uncertainties from sources that are not metabolite-specific (e.g., sampling frequency, flow variability). They and other composite measurands merit consideration from the sewage epidemiology community, beginning with efforts to evaluate the stability of the total cocaine load under realistic sewer conditions.

Quantification of drugs of abuse in municipal wastewater via SPE and direct injection liquid chromatography mass spectrometry

We present an isotopic-dilution direct injection reversed-phase liquid chromatography-tandem mass spectrometry method for the simultaneous determination of 23 drugs of abuse, drug metabolites, and human-use markers in municipal wastewater. The method places particular emphasis on cocaine; it includes 11 of its metabolites to facilitate assessment of routes of administration and to enhance the accuracy of estimates of cocaine consumption. Four opioids (6-acetylmorphine, morphine, hydrocodone, and oxycodone) are also included, along with five phenylamine drugs (amphetamine, methamphetamine, 3,4-methylenedioxy-methamphetamine, methylbenzodioxolyl-butanamine, and 3,4-methylenedioxy-N-ethylamphetamine) and two human-use markers (cotinine and creatinine). The method is sufficiently sensitive to directly quantify (without preconcentration) 18 analytes in wastewater at concentrations less than 50 ng/L. We also present a modified version of this method that incorporates solid-phase extraction to further enhance sensitivity. The method includes a confirmatory LC separation (selected by evaluating 13 unique chromatographic phases) that has been evaluated using National Institute of Standards and Technology Standard Reference Material 1511 Multi-Drugs of Abuse in Freeze-Dried Urine. Seven analytes (ecgonine methyl ester, ecgonine ethyl ester, anhydroecgonine methyl ester, m-hydroxybenzoylecgonine, p-hydroxybenzoyl-ecgonine, ecgonine, and anhydroecgonine) were detected for the first time in a wastewater sample.

Iron(II)-catalyzed oxidation of arsenic(III) in a sediment column

Arsenic contamination in aquatic systems is a worldwide concern. Understanding the redox cycling of arsenic in sediments is critical in evaluating the fate of arsenic in aquatic environments and in developing sediment quality guidelines. The direct oxidation of inorganic trivalent arsenic, As(III), by dissolved molecular oxygen has been studied and found to be quite slow. A chemical pathway for As(III) oxidation has been proposed recently in which a radical species, Fe(IV), produced during the oxidation of divalent iron, Fe(II), facilitates the oxidation of As(III). Rapid oxidation of As(III) was observed (on a time scale of hours) in batch systems at pH 7 and 7.5, but the extent of As(III) oxidation was limited. The Fe(II)-catalyzed oxidation of As(III) is examined in a sediment column using both computational and experimental studies. A reactive-transport model is constructed that incorporates the complex kinetics of radical species generation and Fe(II) and As(III) oxidation that have been developed previously. The model is applied to experimental column data. Results indicate that the proposed chemical pathway can explain As(III) oxidation in sediments and that transport in sediments plays a vital role in increasing the extent of As(III) oxidation and efficiency of the Fe(II) catalysis.