Acute Toxicity and Environmental Risks of Five Veterinary Pharmaceuticals for Aquatic Macroinvertebrates.

Due to the high use of antibiotics and antiparasitics for the treatment of livestock, there is concern about the potential impacts of the release of these compounds into freshwater ecosystems. In this context, the present study quantified the acute toxicity of two antibiotics (sulfadiazine and sulfadimidine), and three antiparasitic agents (flubendazole, fenbendazole, ivermectin) for nine freshwater invertebrate species. These experiments revealed a low degree of toxicity for the sulfonamide antibiotics, with limited implications in the survival of all test species at the highest test concentrations (50 and 100 mg/L). In contrast, all three antiparasitic agents indicated on the basis of their acute toxicity risks for the aquatic environment. Moreover, chronic toxicity data from the literature for antiparasitics, including effects on reproduction in daphnids, support the concern about the integrity of aquatic ecosystems posed by releases of these compounds. Thus, these pharmaceuticals warrant further careful consideration by environmental risk managers.

Process dominance analysis for fate modeling of flubendazole and fenbendazole in liquid manure and manured soil.

Fate monitoring data on anaerobic transformation of the benzimidazole anthelmintics flubendazole (FLU) and fenbendazole (FEN) in liquid pig manure and aerobic transformation and sorption in soil and manured soil under laboratory conditions were used for corresponding fate modeling. Processes considered were reversible and irreversible sequestration, mineralization, and metabolization, from which a set of up to 50 different models, both nested and concurrent, was assembled. Five selection criteria served for model selection after parameter fitting: the coefficient of determination, modeling efficiency, a likelihood ratio test, an information criterion, and a determinability measure. From the set of models selected, processes were classified as essential or sufficient. This strategy to identify process dominance was corroborated through application to data from analogous experiments for sulfadiazine and a comparison with established fate models for this substance. For both, FLU and FEN, model selection performance was fine, including indication of weak data support where observed. For FLU reversible and irreversible sequestration in a nonextractable fraction was determined. In particular, both the extractable and the nonextractable fraction were equally sufficient sources for irreversible sequestration. For FEN generally reversible formation of the extractable sulfoxide metabolite and reversible sequestration of both the parent and the metabolite were dominant. Similar to FLU, irreversible sequestration in the nonextractable fraction was determined for which both the extractable or the nonextractable fraction were equally sufficient sources. Formation of the sulfone metabolite was determined as irreversible, originating from the first metabolite.

Development of a novel concept for fate monitoring of biocides in liquid manure and manured soil taking 14C-imazalil as an example.

Biocides are frequently applied in animal houses for veterinary hygiene or pest control. Thus, they may reach liquid manure tanks. Biocides that are not transformed during manure storage enter soil by the application of manure as organic fertilizer. Due to this environmentally relevant entry route, biocidal substances and products undergo a regulatory fate monitoring in liquid manure and soil. According to this, a novel concept was developed investigating the biocide imazalil as an example. For this purpose, excrements of test animals individually kept in experimental animal houses under standard nutrition were sampled. After matrix characterization, bovine and pig reference manures of defined dry substance contents were prepared. They were used for long-term transformation tests of (14)C-imazalil under strictly anaerobic conditions typical for manure storage in tanks. During the 177-d incubation period, however, imazalil was not substantially transformed. Furthermore, test manures with 7-d aged (14)C-imazalil residues were applied to study aerobic transformation and sorption in manured soil. Both concentration determining processes in soil were affected by the manure matrices. Comparing disappearance times (DT(50)) and sorption coefficients (K(OC)) after standard application (DT(50): 83 d; K(OC): 4059 L kg(-1)), (14)C-imazalil disappeared more rapidly after test manure application. DT(50) values were 29 or 48 d depending on whether bovine or pig test manure was applied. Mobility was slightly enhanced revealed by K(OC) of 1852 and 1385 L kg(-1), respectively.

Chemical and biological characterization of non-extractable sulfonamide residues in soil.

For sulfonamides, the formation of non-extractable residues has been identified by laboratory testing as the most relevant concentration determining process in manured soil. Therefore, the present study has been focused on the chemical and biological characterization of non-extractable residues of (14)C-labeled sulfadiazine or sulfamethoxazole. In laboratory batch experiments, the test substances were spiked via standard solution or test slurry to microbially active soil samples. After incubation periods of up to 102d, a sequential extraction technique was applied. Despite the exhaustive extraction procedure, sulfadiazine residues mainly remained non-extractable, indicating the high affinity to the soil matrix. The remobilization of non-extractable (14)C-sulfadiazine residues was monitored in the activated sludge test and the Brassica rapa test. Only small amounts (<3%) were transferred into the extractable fractions and 0.1% was taken up by the plants. In the Lumbricus terrestris test A, the release of non-extractable (14)C-sulfamethoxazole residues by the burrowing activity of the earthworms was investigated. The residues mainly remained non-extractable (96%). The L. terrestris test B was designed to study the immobilization of (14)C-sulfamethoxazole in soil directly after the test slurry application. The mean uptake by earthworms was 1%. Extractable and non-extractable residues amounted to 5% and 93%, respectively. Consequently, the results of all tests confirmed the high affinity of the non-extractable sulfonamide residues to the soil matrix.

Investigations on the fate of sulfadiazine in manured soil: laboratory experiments and test plot studies.

The fate of 14C-labeled sulfadiazine (SDZ) in manured soil has been investigated in laboratory test systems. In the first approach, stability of 14C-SDZ in liquid bovine manure has been tested. Only 1% of the initially applied radiotracer was mineralized to 14C-carbon dioxide and 82% were transferred to nonextractable residues within a 102-d incubation period. Test slurries with defined aged residues were prepared and, supplementary to standard solutions, applied to silty-clay soil samples. These tests showed the high affinity of 14C-SDZ residues to the soil matrix. In the second approach, basic data on microbial, chemical, and photoinduced degradability in soil were gathered. The data indicated the formation of nonextractable residues as the predominant process in soil, which was accelerated by the test slurry application. In the third approach, laboratory lysimeter tests were conducted to investigate leaching and degradation as simultaneously occurring processes. The 14C-SDZ residues (64%) mainly were retained in the surface layer as nonextractable residues. Although a high mobility in soil was revealed by a soil/water distribution coefficient of 2 L kg(-1), percolate contamination amounted to only 3% of the initially applied 14C-SDZ. The tendencies of leaching and degradability in soil also were observed in test plot studies under field conditions.

Test-plot studies on runoff of sulfonamides from manured soils after sprinkler irrigation.

Three test-plot series have been performed to gather information on runoff of sulfonamides from manured arable and grassland after sprinkler irrigation. To prepare test slurries with defined aged residues, liquid bovine manure was fortified with sulfadiazine, sulfadimidine, and sulfamethoxazole and stored short-term. After test-slurry application, the arable land was treated by soil cultivation before irrigation, and the manured grassland was irrigated directly with 50 mm h(-1) for 2 h. The runoff suspensions were sampled at 5- to 10-min intervals, separated into aqueous phase and suspended matter and residue analyzed. Higher runoff emissions were found from manured grassland plots. The discharge volumes ranged from 106 to 252 L and the total runoff emissions ranged from 13 to 28% of sulfonamides applied initially. Within the first 20 min of the irrigation period that represented a rainfall of 17 mm, emissions, on average, were 4%. The loads of sulfonamides predominantly occurred in the runoff water. The only emissions via suspended matter, on average, were 0.02%. On arable land, however, the runoff was reduced by soil cultivation. Discharge volumes and sulfonamide emissions were 36 to 128 L and 0.1 to 2.5%, respectively. Despite the high-intensity sprinkler irrigation, major emissions did not occur until a 60-min delay.