Understanding the impact of farming on aquatic ecosystems
Download 432.61 Kb.
|
- Navigate this page:
- Faecal pathogens
Veterinary medicinesVeterinary medicines are used widely to treat disease and protect animal health. They include groups of substances such as worming agents, antibiotics, antifungal agents and treatments for ectoparasites. In 2003 the use of veterinary medicines in agriculture represented about 46% of the overall use by market value, with cattle sheep and pig husbandry accounting for 38% and poultry rearing accounting for 8%. The other 54% of the total use of veterinary medicines is associated with the treatment of companion animals (pets).123 Most medicine residues from agricultural sources will be transported into watercourses via direct inputs (e.g. defecation in rivers), surface run-off, contaminated soil transport during storm events, and inputs derived from manure/slurry from intensive livestock rearing units. There is no known information on the total loads and source apportionment of veterinary medicines in surface waters of England and Wales. However, domestic sources are likely to predominate in urban areas whereas water bodies in rural areas are more likely to be at risk from agricultural sources of veterinary medicines where medicine use is concentrated more locally. Medicines in the excreta of domestic pets might be removed at sewage treatment works before they reach a watercourse whereas it is likely that a negligible proportion of agricultural slurry would receive treatment at a sewage treatment works. Some veterinary medicines are toxic to aquatic organisms. For example avermectins and sheep dip chemicals are known to be toxic to organisms at low concentrations (ng l-1 to µg l-1). A number of veterinary medicines also exhibit endocrine disrupting activity. The nature of the impact of veterinary medicines will depend on the type of substance concerned; for example, ectoparasitides will exert their principal effect on insects, whereas the predominant effect of worming agents is likely to be on invertebrates and molluscs. The EA’s Article 5 risk assessments did not consider veterinary medicines. However, the issue of possible environmental impacts of veterinary medicine use in the UK has been addressed in a sequence of research projects carried out by Defra and the Environment Agency.124,125,126,127,128 These had the aim of assessing risk and of prioritising the substances on which monitoring effort and regulatory scrutiny should be concentrated. An initial priority list for further assessment contained 34 compounds from the antibacterial, ectoparasiticide and feed additive groups. For 13 of the compounds, insufficient data were available for ranking purposes in either the terrestrial or aquatic compartments. Using a ranking procedure based on modelling, 18 compounds (amoxicillin, apramycin, bronopol, doramectin, enrofloxacin, eprinomectin, fenbendazole, florfenicol, ivermectin, lincomycin, monensin, moxidectin, oxytetracycline, sulfadiazine, tiamulin, tilmicosin, trimethoprim, tylosin) were identified as worth monitoring in the environment. The procedure identified the medicine treatment scenarios that are most likely to cause harm and the environmental compartments that should be monitored. A monitoring study, based on the results of the ranking, was undertaken over a 11 month period in 2004 to determine concentrations in the UK environment of seven (doramectin, enrofloxacin, ivermectin, lincomycin, oxytetracycline sulfadiazine trimethoprim) of the 18 compounds. Four river sites were selected and targeted to: represent the highest ranked compounds and risk scenarios; have characteristics that would enhance environmental contamination; and, focus on occasions when the compounds were likely to be released to the environment. Overall the results from the study showed that, in general, concentrations of these veterinary medicines were lower than Predicted No Effects Concentrations (PNECs) and were likely to be below those that could affect aquatic and terrestrial organisms. Given that estimates of concentrations in rivers did not raise undue concern and allowing for the greater dilution available, the likelihood of impact in estuarine and marine waters is likely to be low. However, the study identified some areas where future work is warranted. These included: a more detailed assessment of the potential impacts of veterinary medicines on soil; investigations into the fate and effects of parasiticides in sediment; assessment of those compounds that could not be studied in the project due to insufficient data; further assessment of the potential impacts of the other 11 (of the 18) selected veterinary medicines on the environment; monitoring of groundwater. Faecal pathogensThe main pathways that faecal pathogens can be transferred to water bodies are: direct leakage to drainage systems in farmyards; leakage of wastes from buildings and/or stores; run-off from animal manure applications to land; and, direct inputs of faeces into water bodies.129 The transfer of faecal pathogens to water bodies is affected by, for example, soil type, soil water content, rainfall intensity, temperature, topography and agricultural practices. Faecal pathogens from agricultural activities are more of a human health issue rather than having direct impacts on aquatic ecology, primarily because most pathogens are unable to survive for long outside of their host. The EA’s WFD Article 5 risk assessment did not address the impact of faecal pathogens in rivers, lakes or transitional and coastal waters. Modelling of faecal indicator organisms (FIO) inputs into three problem areas (in terms of failing Bathing Water Directive standards) estimated that diffuse agricultural sources contributed around 30% to the total bathing season faecal coliform budget130, although this average figure conceals significant variations in the agricultural contribution to FIO pollution at high and low river flows. This load would contribute to bathing water failures in these problem areas. Two of the three modelled problem areas (North West and South West of England) were associated with flashy river flows and intensively grazed livestock particularly of dairy cows. Download 432.61 Kb. Share with your friends:
|