Prospective aquatic risk assessment for chemical mixtures in agricultural landscapes.

Environmental risk assessment of chemical mixtures is challenging because of the multitude of possible combinations that may occur. Aquatic risk from chemical mixtures in an agricultural landscape was evaluated prospectively in 2 exposure scenario case studies: at field scale for a program of 13 plant-protection products applied annually for 20 yr and at a watershed scale for a mixed land-use scenario over 30 yr with 12 plant-protection products and 2 veterinary pharmaceuticals used for beef cattle. Risk quotients were calculated from regulatory exposure models with typical real-world use patterns and regulatory acceptable concentrations for individual chemicals. The results could differentiate situations when there was concern associated with single chemicals from those when concern was associated with a mixture (based on concentration addition) with no single chemical triggering concern. Potential mixture risk was identified on 0.02 to 7.07% of the total days modeled, depending on the scenario, the taxa, and whether considering acute or chronic risk. Taxa at risk were influenced by receiving water body characteristics along with chemical use profiles and associated properties. The present study demonstrates that a scenario-based approach can be used to determine whether mixtures of chemicals pose risks over and above any identified using existing approaches for single chemicals, how often and to what magnitude, and ultimately which mixtures (and dominant chemicals) cause greatest concern. Environ Toxicol Chem 2018;37:674-689. © 2017 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Aerobic degradation of tylosin in cattle, chicken, and swine excreta.

Tylosin, a fermentation-derived macrolide antibiotic, was tested to determine its aerobic degradation rate in cattle, chicken, and swine excreta. For chicken, excreta from a hen administered 14C-tylosin as part of a metabolism study were used. For cattle and swine, 14C-tylosin was added to control excreta. The formation of 14C volatile breakdown products and 14CO2 was not observed throughout the study. Material balance for the carbon-14 label ranged between 94% and 104%. Initial, day-0, concentrations of tylosin-A averaged 119.52+/-4.39, 35.01+/-1.34, and 62.82+/-2.11 microg/g (dry weight basis) for cattle, chicken, and swine excreta samples, respectively. After 30 days, samples averaged 4.16+/-0.69 and 4.11+/-0.69 microg/g tylosin-A in cattle and swine excreta, respectively. No residues of tylosin-A or its factors were apparent in the chicken excreta samples after 30 days of incubation. In each case, tylosin declined to less than 6.5% of the initial level after 30 days. Calculated first-order half-lives under the test conditions were 6.2 days, <7.6 days, and 7.6 days for cattle, chicken, and swine excreta, respectively. The results indicate that tylosin residues degrade rapidly in animal excreta. Therefore, tylosin residues should not persist in the environment.

Environmental fate and chemistry of raloxifene hydrochloride.

Raloxifene hydrochloride is a selective estrogen receptor modulator (SERM) used for the prevention and treatment of osteoporosis in women. Excretion of raloxifene occurs through the feces of patients. Raloxifene has the potential to be discharged into waste treatment systems after therapeutic use. Raloxifene hydrochloride was investigated using a battery of studies designed to describe its physical/chemical characteristics and define its fate in the environment. The mean measured solubility of raloxifene hydrochloride (+/- standard deviation) was 345.2 +/- 15.6 microg/ml, 13.3 +/- 0.6 microg/ml, 0.9224 +/- 0.015 microg/ml, and 627.4 +/- 132.0 microg/ml in aqueous buffers at pH 5, 7, and 9 and in unbuffered water, respectively. Raloxifene exhibited a mean molar absorptivity of 34,000 and a wavelength absorbance maximum at 287 nm for pH 5 and 7 aqueous buffer solutions and 297 nm at pH 9. Mean measured Kow values were 516 +/- 17, 1,323 +/- 91, and 1,556 +/- 135 at pH 5, 7, and 9, respectively. After 5 d at 50 degrees C, raloxifene hydrolyzed 8.02, 10.61, and 23.81% in pH 5, 7, and 9 aqueous buffers, respectively. In a 28-d hydrolysis study at 25 degrees C, the calculated first-order hydrolysis rates were 6.92 x 10(-4), 1.70 x 10(-3), and 7.66 x 10(-3)/d, and the corresponding half-lives were 1,001, 410, and 90 d in pH 5, 7, and 9 aqueous buffers, respectively. Raloxifene sorbed significantly to sewage treatment solids with Freundlich isotherm adsorption coefficients K between 2,000 and 3,000. Raloxifene degraded rapidly in the presence of sewage solids. In a system containing 0.470 g/L sludge solids, the raloxifene biodegradation rate and half-life were 0.0966/h and 7.17 h, respectively. In a 28-d aerobic-aquatic biodegradation study containing 30 mg/L sludge solids, the raloxifene biodegradation rate and half-life were 0.0188/d and 37 d, respectively. Given the fate and behavior of raloxifene in these studies, it is anticipated that raloxifene would rapidly dissipate in the environment.