Otters found dead on our roads are providing important new information on the ecology of this secretive species - and evidence of how successful the ban on lead in petrol has been in reducing levels of lead pollution. Speaking at the British Ecological Society's Annual Meeting next week, Dr Liz Chadwick of Cardiff University's Otter Project will report the results of collaborative research with Cornwall's Wildlife Veterinary Investigation Project. Both have been conducting post mortems on otters killed by cars and reported by members of the public since 1992, in an initiative funded by the Environment Agency.

"We measured the level of lead in rib-bones taken from over three hundred otters found dead in south-west England between 1992 and 2004, collected by wildlife veterinary pathologist Vic Simpson. We compared this with levels of lead found in stream sediment by the British Geological Society, and airborne emissions recorded by the National Atmospheric Emissions Inventory. While some variation related to geology, we found an extremely strong decline over time, reflecting declining emissions from car fuel: otter bone lead levels in 2004 were less than a quarter of those in 1992," Dr Chadwick will tell the meeting in Oxford.

Legislation halved the amount of lead in petrol in 1986 and phased out general use of leaded petrol in 1999, and atmospheric lead emissions have declined as a result. But although lead emissions have declined, ecologists did not know whether this fall in airborne lead levels was reflected in aquatic ecosystems. In northern Europe the otter is the dominant predator of freshwater food chains, and so levels of pollutants in otter tissues can be a useful indicator of pollution in the environment in which it feeds.

According to Dr Chadwick: "Our results show that what we do in terms of legislative control on pollutants really works - declines in lead in the atmosphere have been dramatic, and have been followed by declines of this heavy metal in the otter - a species of considerable conservation concern. The fact that levels have declined in the otter means that levels have almost certainly declined throughout the aquatic food chain - as top predator, otter tissues provide an indication of intake further down the food chain."

The results also have important implications for human health. "Reductions in environmental lead levels are good news. In humans, lead can damage the central nervous system including the brain; it also affects the kidney, and reduces growth - particularly in children. These effects on human health provided the impetus behind legislative controls. While it is not possible to measure most of these factors in the otter, similar effects have been shown in other mammals, and it is likely that lower lead levels are related to a healthier otter population."

The research highlights the importance of long-term monitoring and archiving of samples, and shows that with the help of the public, valuable use can be made of undesirable events such as wildlife road traffic accidents.

Dr Chadwick will present her findings at 10:30 on Thursday 7 September 2006 at the British Ecological Society Annual Meeting

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