Biodegradability of metronidazole, olaquindox, and tylosin and formation of tylosin degradation products in aerobic soil--manure slurries.

The use of veterinary drugs (primarily antibiotics) in animal husbandry harbors the risk that these compounds end up in the farmland when manure is used as fertilizer. The biodegradability of three compounds, olaquindox (OLA), metronidazole (MET), and tylosin (TYL), was simulated in soil--manure slurries with 50 g of soil per liter. Supplemental batch sorption tests revealed that insignificant amounts of OLA and MET were located in the soil phase, whereas only 0.1 to 10% of the added amounts of TYL remained in the liquid phase. This may reduce the bioavailability and thus biodegradation rates of TYL. Unidentified metabolites of OLA and TYL and four known TYL metabolites were detected using HPLC. However, none of these substances were seen to persist in the biodegradation experiments, indicating that OLA and TYL most likely were mineralized in the experiments. Neither the use of sandy or clayey soil nor the use of 0, 1, or 10% (V/V) of manure added to these soils had a significant effect on the degradation rates. Degradation half-lives for the primary degradation were 3.3--8.1 days for TYL, 5.8--8.8 days for OLA, and 13.1--26.9 days for MET. Based on comparisons of results obtained with the benchmark chemical aniline and degradation half-lives of this compound in nature, it was assessed that results obtained with the current test method slightly overestimate real-world biodegradation rates.

Biodegradability of the molluscicidal saponins of Phytolacca dodecandra.

The biodegradability of water-extracted saponins of berries from the Endod plant, Phytolacca dodecandra L'Herit, was evaluated under OECD standardized conditions. Persistence of the saponins was evaluated by determination of saponin concentrations in water over a 30-day period, using a quantitative HPLC method and a semiquantitative hemolytic assay, which is considered a potential field method. The two methods were compared. Bioassays were simultaneously conducted using Biomphalaria glabrata fresh water snails to assess the molluscicidal potency over time. All experiments were carried out in water, which was chemically balanced to sustain snails, and to one set river water was added to the medium to mimic natural conditions. (1) Saponin concentrations in water treated with an aqueous extract of P. dodecandra cultivar E44 were stable for 2 days then rapidly decreased during the third and fourth day. Lethal concentrations to snails were LC50 = 9.6 mg/l (95% CI: 6.3 to 19.4) in one set and LC50 = 6.8 mg/l (95% CI: 5.4 to 12.2) in the other. Adding river water to one set of the experiments had no effect on the mean saponin concentration over time (F = 0.02, P = >0.05). (2) Comparison of the hemolytic assay with the HPLC method showed no significant difference in mean saponin concentrations (t = 0.32, P > 0.05, 95% CI: -2.67 to 3.64), and a correlation of r2 = 0.88 between the two methods. (3) The saponin fraction of an aqueous extract of P. dodecandra was readily biodegraded (t1/2 = 15.8 h), and the complete consumption within a 10-day window indicates ready degradability in aquatic environments under aerobic conditions. (4) These results show that the use of Endod berries for snail control in schistosomiasis-infested water bodies is environmentally acceptable.