The report evaluates the results of PCB and dioxin monitoring in and around the ReChem site in spring 1993. This was carried out in response to recommendations in a study last year which concluded that it had been shown "beyond reasonable doubt" that PCB and dioxin contamination within 500 metres of the plant had been caused by ReChem's operations, despite the firm's claims to the contrary (ENDS Report 220, p 11 ).
Last year's report showed that PCB levels in soils close to the plant were up to 20 times higher than in areas remote from the site, while PCB levels in air were about 100 times higher close to the site than at a nearby rural location. Dioxins showed a similar pattern.
The latest study, carried out, like its predecessor, by the School of Environmental Sciences at the University of East Anglia, was designed to delineate more precisely the extent of the main area of contamination to the south and east of the incinerator. Soil and air sampling was carried out in February and March 1993.
As before, the soil analyses indicated a declining gradient in PCB concentrations away from the incinerator. The mean PCB level on ReChem's site was 1,630µg/kg, falling to 232µg/kg in a field bordering the site, and to 101µg/kg in a largely residential area further east.
For comparison, the report cites 40µg/kg as a quite common PCB level in UK urban soils, with levels of 100µg/kg being not uncommon in industrial areas. Soils with PCB levels in excess of the latter figure are confined to land within 200 metres of ReChem's eastern site boundary. The pattern of dioxins in soils was again found to be similar.
Both PCB and dioxin levels in air were found to be lower last year than in 1992. Mean PCB levels in the field adjacent to the site's eastern boundary, for example, were 15.5ng/m3 in 1992 but 5.8ng/m3 last year.
However, it is far from clear that this was a real reduction. Firstly, winds blew from the west and south-west for only 17% of the time during last year's air sampling operation, compared to 50% of the time in 1993. Secondly, the lower temperatures during last year's sampling compared to 1992 - when PCBs in air were measured between March and August - would have caused less PCB volatilisation from sources on ReChem's site.
Thirdly, at no point during the studies has any attempt apparently been made to relate changes in ReChem's waste inputs, operating practices and abatement techniques to emissions from the works. Although no other UK plant has been subject to such in-depth investigation, this shortcoming reduces the value of the findings - not least because major changes in ReChem's PCB inputs are known to have occurred since the mid-1980s.
The study shows that PCB levels in air immediately adjacent to the ReChem works were at least six times higher in 1993 than the values found in urban areas. Most of the dioxin results for this site were also above the highest of the values found in UK cities.
The study concludes, however, that the contamination is of little significance for human health. On a worst case scenario, the largest contribution relative to an officially recommended tolerable intake would occur if a child ingested soil with the highest dioxin values from the field next to the incinerator. The maximum dioxin intake from this source would be about 25% of the tolerable level. Monitoring of locally grown food, another possible pathway for PCB and dioxin exposure in humans, is due to be completed later this year.