Reduced antimicrobial potencies of oxytetracycline, tylosin, sulfadiazin, streptomycin, ciprofloxacin, and olaquindox due to environmental processes.

The stability of oxytetracycline (OTC), tylosin (TYL), sulfadiazin (SDZ), streptomycin (ST), ciprofloxacin (CF) and olaquindox (O) was examined in environmentally relevant matrices, such as soil interstitial water and sewage sludge water. Compounds were assessed in both aerobic (OTC, TYL, SDZ, ST, and CF) and anaerobic experiments (OTC, TYL, and O) using analytical measurements (UV spectrophotometry or HPLC) combined with a growth inhibition pour plate assay using activated sludge bacteria. (OTC was additionally assessed using a soil bacterial assay.) This combination of results enabled the assessment of whether a loss in antibacterial potency was reflected in a similar reduction of substance concentration. If a potency reduction is not reflected in a decreased substance concentration, the results may indicate the formation of less potent degradation products possessing the same chromophoric system (same UV absorbance maximum) as the parent compound. With the exception of ST and CF, the antimicrobial agents generally lost a considerable amount of their antimicrobial potency in aerobic experiments. In the anaerobic experiments having either an experimental duration of 21 or 100 days only OTC retained potency. These results correspond well with the fact that several degradation products were encountered in the study for this compound

Primary biodegradation of veterinary antibiotics in aerobic and anaerobic surface water simulation systems.

The primary aerobic and anaerobic biodegradability at intermediate concentrations (50-5000 microg/l) of the antibiotics olaquindox (OLA), metronidazole (MET), tylosin (TYL) and oxytetracycline (OTC) was studied in a simple shake flask system simulating the conditions in surface waters. The purpose of the study was to provide rate data for primary biodegradation in the scenario where antibiotics pollute surface waters as a result of run-off from arable land. The source of antibiotics may be application of manure as fertilizer or excreta of grazing animals. Assuming first-order degradation kinetics, ranges of half-lives for aerobic degradation of the four antibiotics studied were 4-8 days (OLA), 9.5-40 days (TYL), 14-104 days (MET) and 42-46 days (OTC). OLA and OTC were degraded with no initial lag phase whereas lag phases from 2 to 34 days (MET) and 31 to 40 days (TYL) were observed for other substances. The biodegradation behaviour was influenced by neither the concentrations of antibiotics nor the time of the year and location for sampling of surface water. Addition of 1 g/l of sediment or 3 mg/l of activated sludge from wastewater treatment increased the biodegradation potential which is believed to be the result of increased bacterial concentration in the test solution. Biodegradation was significantly slower in tests conducted in absence of oxygen. Assessments of the toxic properties of antibiotics by studying the influence on the biodegradation rates of 14C-aniline at different concentrations of antibiotics showed that no tests were conducted at toxic concentrations.

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.

Environmental risk assessment of antibiotics: comparison of mecillinam, trimethoprim and ciprofloxacin.

The effects of mecillinam, trimethoprim and ciprofloxacin, antibiotics used in the treatment of urinary tract infections, on the aquatic environment were assessed. Mecillinam and ciprofloxacin were both readily biodegradable (primary degradation) in activated sludge, whereas trimethoprim persisted. The toxicity of these antibiotics towards sludge bacteria, a green alga, a cyanobacterium, a crustacean and a fish were investigated; both mecillinam and ciprofloxacin were highly toxic to the cyanobacterium Microcystis aeruginosa (EC50 in the range 5-60 microg/L). Risk characterization for the aquatic environment was performed for the three compounds by calculating the predicted environmental concentration (PEC) and the predicted no-effects concentration (PNEC). A PEC/PNEC ratio of <1 indicates that, with the present pattern of use, no environmental risk is expected. PEC/PNEC ratios of <1 for present usage in Europe were found for mecillinam and trimethoprim whereas a PEC/PNEC ratio >1 was found for ciprofloxacin.

Environmental risk assessment of antibiotics: comparison of mecillinam, trimethoprim and ciprofloxacin.

The effects of mecillinam, trimethoprim and ciprofloxacin, antibiotics used in the treatment of urinary tract infections, on the aquatic environment were assessed. Mecillinam and ciprofloxacin were both readily biodegradable (primary degradation) in activated sludge, whereas trimethoprim persisted. The toxicity of these antibiotics towards sludge bacteria, a green alga, a cyanobacterium, a crustacean and a fish were investigated; both mecillinam and ciprofloxacin were highly toxic to the cyanobacterium Microcystis aeruginosa (EC(50) in the range 5-60 Ìg/L). Risk characterization for the aquatic environment was performed for the three compounds by calculating the predicted environmental concentration (PEC) and the predicted no-effects concentration (PNEC). A PEC/PNEC ratio of <1 indicates that, with the present pattern of use, no environmental risk is expected. PEC/PNEC ratios of <1 for present usage in Europe were found for mecillinam and trimethoprim whereas a PEC/PNEC ratio >1 was found for ciprofloxacin.

Shake-flask test for determination of biodegradation rates of (14)C-labeled chemicals at low concentrations in surface water systems.

A simple shake-flask surface water biodegradability die away test with (14)C-labeled chemicals added to microgram per liter concentrations (usually 1-100 microg/L) is described and evaluated. The aim was to provide information on biodegradation behavior and kinetic rates at environmental (low) concentrations in surface water systems. The basic principle of measurement was to determine evolved CO(2) indirectly from measurements of total organic activity in subsamples after stripping off their content of CO(2). Used with surface water alone the test simulates a pelagic environment and amended with sediments (0.1-1 dry weight/L) the test is intended to simulate a water environment with suspended solids (e.g., resuspended sediments). A protocol of the test used with the (14)C technique or with specific chemical analysis was recently developed by the International Organization for Standardization. Practical experience with the method is presented for a set of reference substances. These substances could be ranked in five groups of decreasing biodegradability: aniline>p-nitrophenol, 2, 4-dichlorophenoxyacetic acid>4-chloroaniline>maleic hydrazide, pentachlorophenol>atrazine. It was found that degradation rates and lag periods varied considerably among sampling sites and sometimes also among samples from the same site. No significant correlation could be established between degradation rates and microbial biomass estimates. Even small portions of added sediments greatly enhanced biodegradation of the absorbable compound pentachlorophenol, probably by providing sites for microbial attachment. Repeated tests indicated consistent degradation behavior for the readily degradable substances, whereas degradation sometimes stopped or failed with the more recalcitrant substances. A preadaptation step involving regular reinoculation with freshly collected surface water could, however, overcome the problems of false-negative results.

Stability of Tylosin A in manure containing test systems determined by high performance liquid chromatography.

Tylosin is a widely used antibiotic for the treatment of infections in swine. Tylosin consists of a mixture of Tylosin A, Tylosin B, Tylosin C and Tylosin D. All components contribute to the potency of tylosin but Tylosin A is by far the major component (usually about 90% and not less than 80%). A fast, robust and easily performed HPLC method has been developed for determination of Tylosin A in the presence of tylosin residues; Tylosin B, Tylosin C and Tylosin D in manure containing incubation media. The separation was performed using a YMC-Pack ODS-AQ column (250 x 4.6 mm i.d., 5 microns particle size) operated at 35 degrees C. The mobile phase consisted of 2.25% (w/v) sodium perchlorate pH 2.5-acetonitrile (60:40 v/v). Detection was performed by measuring the UV absorption at a wavelength of 290 nm. Calibration curves of tylosin made in the incubation medium containing 6.4% manure were linear in the range from 0.375 to 128.0 mg/l (R2 = 0.999). The limit of quantitation (at the RSD 20% level) for Tylosin A was found to be 0.4 mg/l in incubation media containing 6.4% manure. The recovery of Tylosin A was in the range from 100% to 108% depending on the concentration of manure. The reproducibility was good as the relative standard deviation (n = 4) in each matrix tested was in the range from 0.7 to 1.9 at the 25 mg/l level. The stability of Tylosin A was studied under methanogenic conditions and the half-life was found to be less than two days. Studies under aerobic conditions showed that the degradation rate was found to increase with increasing concentrations of manure particles in the incubation medium. It is, however, not clear whether the decrease in the concentration of Tylosin A is caused by sorption, abiotic or biotic chemical degradation. The major degradation product of Tylosin A in methanogenic as well as aerobic incubation media has a UV-spectrum and a retention time corresponding to Tylosin B. Furthermore, Tylosin D is believed to be a minor degradation product.

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.

Occurrence, fate and effects of pharmaceutical substances in the environment--a review.

Medical substances (pharmaceuticals) are a group of substances that until recently have been exposed to the environment with very little attention. The reason why they may be interesting as environmental micropollutants, is that medical substances are developed with the intention of performing a biological effect. Especially antibiotics used as growth promoters, as feed additives in fish farms are anticipated to end up in the environment. Very little is known about the exposure routes of the medical substances to the environment. Only few investigations have reported findings of medical substances in other field samples than sediment or treated waste water samples. Several substances seem to be persistent in the environment. This paper outlines the different anticipated exposure routes to the environment, summarises the legislation on the subject and gives an outline of present knowledge of occurrence, fate and effect on both the aquatic and terrestrial environments of medical substances. Present knowledge does not reveal if regular therapeutic use may be the source of a substance carried by sewage effluent into the aquatic system, even though clofibrate, a lipid lowering agent, has been identified in ground and tap water samples from Berlin. Further research would be necessary to assess the environmental risk involved in exposing medical substances and metabolites to the environment.

Estimation of kinetic rate constants for biodegradation of chemicals in activated sludge wastewater treatment plants using short term batch experiments and microgram/L range spiked concentrations.

Biodegradation rate constants that are believed to be predictive for activated sludge sewage treatment plants have been determined at microgram/L concentration levels using short term (hours) laboratory scale batch experiments with activated sludge. Rate constants were estimated for four model chemicals with widely different biodegradability characteristics, and experiments were conducted with sludges of various origin and treatment. Test substances were applied at concentrations ranging from a few microgram/L for deriving first order rate constants and up to several mg/L for full investigation of the kinetics. Model substances were acetate, aniline, 4-chloroaniline and pentachlorophenol and their biodegradation was assessed by means of 14C tracer technique. Some experiments included test concentrations equal to those prescribed in standard biodegradability tests (20 mg DOC/L). Sludge types investigated included adapted and non-adapted sludge from laboratory scale semicontinuous reactors as well as sludges collected from a pilot scale sewage treatment plant loaded with predominantly domestic sewage. At low chemical concentrations ( < approx. 100 micrograms/L) first order degradation rate constants were reasonably constant and varied only little with the applied concentration. With aniline, however, elimination rates increased at concentrations below about 20 micrograms/L, probably because transient sorption became significant. At higher concentrations absolute (linear) degradation rates could be described by saturation kinetics, and for aniline a half saturation constant, K(S), was estimated at 3 mg/L. "Best estimates" of average first order rate constants in the low concentration regime measured with 3 g SS/L and at 22 degrees C were: acetate, 8 h-1; aniline, 0.8 h-1, 4-chloroaniline, 0.15 h-1, and pentachlorophenol, 0.01 h-1 (non adapted sludge) or 0.02 h-1 (adapted sludge). These figures seem to agree well with standard or default biodegradation rate constants for sewage treatment plants suggested in a European Union technical guidance document for chemical risk assessment, which is currently under preparation.