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4.4 Health of the environment
EutrophicationConcentrations in Welsh rivers of the main plant nutrients (phosphate and nitrate) are generally much lower than those found in the midlands and south-east England. There are correspondingly fewer perceived problems associated with eutrophication compared with lowland England. However, nutrient enrichment arising from sewage inputs and agriculture does cause water quality problems in all types of aquatic environment, affecting drinking water supplies, conservation interests and recreational uses. A number of water-supply reservoirs are regularly affected by blue-green algal blooms notably Llandegfedd, Wentwood, Cefni and Nant-y-Frith, with implications for water treatment and supply. Conservation interests are being affected at a number of important wetland sites on Anglesey, at Bosherston Lakes in south Pembrokeshire and at Llangorse Lake near Brecon. Eutrophication is affecting the survival of two endangered fish species: the gwyniad in Llyn Tegid and the arctic charr in Llyn Padarn. Blooms of blue-green algae can interfere with recreational activities at a number of waters, including Llysyfran Reservoir and Eglwys Nunydd. Despite the environmental safeguards to deal with the consequences of eutrophication specified in the Cardiff Bay Barrage Act, algal blooms are likely to affect recreational uses and aesthetic enjoyment within the impoundment.
In general, scientific understanding of the links between nutrient inputs and eutrophication in estuarine and coastal waters is much less advanced than for freshwaters. Nevertheless, eutrophication appears to be connected with periodic low concentrations of dissolved oxygen in the Loughor and Dee estuaries. The impoundment created by the Tawe Barrage in Swansea is subject to blooms of marine algae, and the impoundment has already been designated as a sensitive area.
Blooms of toxic marine algae are relatively rare around the Welsh coast although blooms of the dinoflagellate Gyrodinium aureolum have been linked to fish and shellfish mortalities in Swansea Bay in 1989 and St. Brides Bay, Pembrokeshire in 1994. Other blooms of potentially toxic alga include the dinoflagellate Alexandrium tamarense which has been recorded in the upper part of Milford Haven since 1995, and a bloom of Dinophysis was recorded within the Tawe impoundment in 1995. The former can produce Paralytic Shellfish Poisoning and the latter Diarrhetic Shellfish Poisoning, but no effects on human health have been observed to date. Synthetic chemicalsThe distribution of individual synthetic chemicals in the Welsh environment reflects their physical and chemical properties, and the way in which they are dispersed. The persistent substances are poorly soluble in water but soluble in fat. They therefore attach to sediment particles, accumulate in the fatty tissues of animals, and pose the greatest risk to animals at the top of food chains. In freshwater these are fish-or insect-eating aquatic birds and aquatic mammals, such as otters, and in the marine environment seals, porpoises, dolphins and seabirds are at greatest risk. Clearly humans are also at potential risk from the consumption of contaminated wild animals. The techniques for monitoring distribution and measuring the effect of these chemicals are difficult and expensive. Consequently only the apparent high priority chemicals have received attention so far, and techniques are still being developed for many groups of synthetic pollutants. PCBs PCBs have been found to be present in freshwater eel tissue at sites throughout Wales, but highest concentrations were found in the lower reaches of industrialised catchments in the south-east and north30. Aerial inputs derived from global sources may also be a significant route for PCBs found in dipper eggs (an insectiverous riverine bird) at remote rural sites31. In the marine environment, contamination is related to past industrial production, use, disposal and subsequent transport with fine sediment. Marine sediments are‘heavily contaminated’ close to river mouths and docks in the Severn Estuary/Bristol channel, ‘contaminated’ at offshore sites in the Severn Estuary and Swansea Bay, and ‘slightly contaminated’ in the centre of the Bristol Channel32. Although fish from Cardigan Bay and the Severn Estuary do not appear to be seriously contaminated, high concentrations have been found in marine mammals from these locations. This appears to be evidence of high accumulation in predators at a considerable distance from PCB sources. Dioxins The greatest risk of contamination by dioxins/furans is near potential sources such as waste incinerators. The Welsh Office commissioned a study of dioxins/furans and PCBs in the environment around the high-temperature incineration plant of Rechem at Pontypool in 199133. With the exception of a localised area within 500m of the plant, measured concentrations of PCBs and dioxins/furans in the environment provided little evidence of levels of contamination any different from those encountered in similar areas elsewhere in the UK. The effects of this plant should not give rise to undue concern, according to accepted criteria and guidance on health effects for these compounds. Pesticides Organochlorine pesticides were used for a wide range of applications in Wales, sheep dipping and wool preparation being the main rural use. Use of dieldrin and DDT in the UK was banned in the late 1980s, but significant residues of these pesticides remain in eels from agriculture-intensive and industrialised catchments. In the marine environment they are still found in the fatty tissues of marine mammals, and an inshore Cardigan Bay sediment sample contained the highest level of dieldrin contamination of all sites in a national survey35. Pentachlorophenol was synthesised in Wales and is still found in the discharge from the manufacturing site, although production ceased many years ago. Residues remain in sediments surrounding the discharge, and a slight effect on the invertebrate community there is evident. The biological impacts of organophosphate and synthetic pyrethroids are covered in Section 4.2. PAHs Polycyclic aromatic hydrocarbons (PAHs) that result from combustion of fossil fuels and waste material are found widely in industrialised areas, in road run-off and in marine sediments close to shorelines. Many are moderately persistent in the environment, but are broken down in fish and higher vertebrate animals. They can cause the same sorts of cellular effects as PCBs and dioxins. Organotin Use of tributyltin (TBT) antifouling paint on boats less than 25m in length ceased in 1987, and the application and removal of such paints on boats of 25m or more became subject to regulation in 1996. Evidence of impact on the affected species (dog whelk) is limited to parts of Milford Haven and Holyhead harbour, close to current sources of TBT on large vessels35. Organotin compounds have been used in other applications and their well-documented endocrine disruptive effect may require further assessment. Radioactivity
In June 1998, the Welsh Office announced a targeted testing programme for four areas at the highest risk from radon gas emitted by natural sources. Householders in these areas can receive detectors from the NRPB to monitor radon gas in their properties over a three-month period. The need for measures to reduce levels will then be evaluated. Grants to assist in this work may be available from local authorities. New homes are protected through the building requirements in high-radon areas. The results of extensive monitoring of the effects of nuclear facilities on levels of radiation in the environment are reported annually by MAFF. This includes an assessment of the maximum exposure to radiation to humans from each source. For terrestrial sources, these assessments are generally based on concentrations in agricultural produce local to the nuclear facility. For aquatic foodstuffs, the assessment is based on concentrations in species commonly harvested for human consumption. The calculation of the dose received is based on consumers with the highest potential intake of the food in question37. The exposure from each of the nuclear facilities in Wales was a small percentage of the maximum limit (1 millisievert) for members of the public from artificial sources of radiation (Figure 4.20). Monitoring in 1998 of the impact of the discharges from Amersham in Cardiff established that there were relatively high concentrations of tritium in flounders (up to 50,000 bequerels/kilogram) caught near the effluent discharge from the plant and also in sediments within the Severn Estuary. Previously it had been assumed, in accordance with other studies, that concentrations in fish would be similar to that of ambient seawater. The finding that tritium could be bioaccumulated required a reassessment of the radiation dose to the critical group of fish consumers in Cardiff, and the 1997 figure of 3% has been revised to 6%. This is still a small proportion of the dose limit but nevertheless the unexpected bioaccumulation of tritium was of concern and resulted in a requirement for tritium discharges to be reduced significantly (see Section 5.7). A survey was undertaken in 1997 to determine the concentration of technetium-99 in selected animals and plants around the Welsh coast. Highest concentrations (1836 bequerels/kilogram) were found in brown seaweed at sites closest to the Sellafield discharge along the north Wales coast. Concentrations decreased southwards with lowest amounts present at sites in the Bristol Channel. The highest concentration found in periwinkles in the same survey was 152 bequerels/kilogram. This is not a high concentration in relation to the risk to human health since consumption of 12 kilograms would result in a radiation dose of 1 microsievert, which is only 0.1% of the dose limit. Acid rain
Cuts in sulphur emissions have reduced deposition in upland Wales from 30–50 kg/ha/year in 1984 to 20–30 kg/ha/year in 1995. Cuts in emissions of oxidised nitrogen have also contributed to reducing the affected area, but substantial further progress is needed25. The effects of reductions to date are apparent in declining sulphate concentrations and slight reductions in the acidity of 77 streams surveyed in 1984 and 1995. However, these improvements have not yet led to biological recovery (Section 4.2). |
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