Understanding the impact of farming on aquatic ecosystems
Endocrine disrupting chemicals
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Endocrine disrupting chemicalsA range of chemicals have been shown to have the potential to adversely affect the endocrine systems of invertebrates and vertebrates. These include natural hormones, synthetically produced hormones and other man-made chemicals such as some pesticides and some plastic additives. The main pathways that would potentially lead to impacts on aquatic ecosystems would, therefore, depend upon the activities and uses associated with any particular endocrine disrupting chemical. The substances that have been identified as presenting the greatest potential impact on freshwater ecosystems are steroids, including the natural steroids (oestrone, oestradiol and oestriol) and the synthetic steroid ethinyloestradiol. However it should be noted that although invertebrates represent approximately 95% of all species, knowledge of the endocrinology of many taxonomic groups is limited and the vast majority of research carried out to date has focused on chemical-induced effects on vertebrates. Natural steroids from farming can enter water bodies by either point or diffuse sources with the main pathways being: direct inputs (urine/faeces) from animals into water bodies; leakage and run-off from slurry stores and from hard-standings in farm areas; and runoff from direct deposits of urine and faeces on land, and run-off from slurries and manures applied to land. Run-off from land has been considered to be the least significant pollution pathway for steroid hormones because of degradation and adsorption of the substances in soil 141. Other chemicals associated with farming-related activities (e.g. atrazine) have been shown to possess endocrine disrupting activity but these effects have been considered in the derivation of EQSs. Evidence from other European countries suggests that agriculture is the main source of oestrogens excreted.142 In the Netherlands it has been estimated the total steroid oestrogen excretion by all domestic animals and humans is 49.6 kg day-1, with farm animals accounting for 94% and humans for 6%. Among farm animals, pregnant cows and breeding female pigs contributed the greatest volume of natural steroid oestrogens (22 and 10.6 kg day-1 respectively). The extent of the impact on steroids on a particular receiving water body will obviously depend on the relative populations of humans and animals in that catchment. In this context it also needs to be recognised that whilst releases of steroids from humans will be treated at sewage treatment works before discharge to water bodies, releases from farm animals can directly enter water bodies. Most studies of hormones in rivers have focused on inputs from sewage treatment works, and their consequences for endocrine disruption in fish. However, in areas where there is intensive livestock rearing, excretion by farm animals can also contribute to the natural steroid oestrogen load in the environment.143,144,145 The EA has carried out a critical evaluation of the numerous ecotoxicological studies that have been undertaken for the natural steroids and the synthetic steroid ethinyloestradiol.146 Based on this review, a ‘tentative’ Proposed No Effects Concentrations (PNEC) value for the natural steroid 17β-oestradiol of 1.0 ng l-1 was proposed given that 17β-oestradiol can cause adverse effects in the 10-50 ng l-1 range for a variety of species. No PNECs were proposed for oestrone and oestriol, which are know to be less potent endocrine disrupters than oestradiol. At present there is only limited data on the concentrations of agriculturally related endocrine disrupting chemicals (excluding pesticides) in UK fresh and marine waters. A recent study conducted for Defra investigated the extent of steroid hormone contamination in streams associated with livestock farms.147 The majority of the 10 sites selected were streams running through dairy farms, although some examples of beef, sheep and pigs were included. The sites were selected to represent worst case conditions where, for example, small streams passed through intensive livestock farms, soil types and topography were favourable to the transfer of substances and animals had access to the streams. An experimental farm was also included, making 11 sites in total. Ninety-two percent of the monitoring stations gave measurable oestrogenic activity, and on 8 of the 11 farms surveyed oestrogenic activity exceeded at least once the PNEC for 17β-oestradiol in water. The data do not allow clear discrimination between different livestock sources, but spreading of cattle slurry and run-off from farmyards may be more important than direct excretion to farmland or streams. Overall, both the Yeast Estrogen Screen (YES) bioassay and chemical analytical data were taken to indicate that fish in headwater streams on or near some livestock farms may be at risk of endocrine disruption from steroids (i.e. there would be exceedances of the PNEC). In terms of the likely contamination pathways, it was noted that as long as good agricultural practice is followed then the risk to watercourses from farming-related activities should be minimal and that humans are the primary source in UK rivers. However, poor farming practice (e.g. direct excretion of livestock into unfenced streams, direct run-off from slurry stores and farmyards) may lead to significant steroid hormone pollution.148 Endocrine disrupting chemicals, whose effects may have been masked in the past by the presence of gross pollution, are now recognised as having the potential to affect the viability of coarse fish populations.149 The most evident effect is intersex in male fish. Typically males exhibit female-like characteristics, possessing female oviducts and eggs within the testes. Such effects have been shown to be permanent, progressive and can lead to reduced reproductive performance. Whilst initial research programmes focused on a limited number of highly impacted sites receiving treated sewage effluent150151, a more recent survey (2002/2003) was conducted to establish a more comprehensive view of the spatial extent and severity of oestrogenic effects in wild fish (roach) in English and Welsh rivers again primarily in relation to discharges of sewage effluent.152 A further objective of the latest survey was to review predictions of impacts on fish at high, medium and low risk sites, based on predicted oestrogenic activity of the sewage effluents. Intersex roach were found at 44 (86%) of the 51 sites surveyed in 5 Agency regions. In addition, some roach populations where sewage treatment effluents were low or absent showed no observable intersex effects. Further work is required to understand the implication of endocrine disruption on the populations of roach and other fish populations in relation to all potential sources (sewage treatment works effluent and farming). Download 432.61 Kb. Share with your friends:
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