POLYNUCLEAR AROMATIC-HYDROCARBONS IN THE UNITED-KINGDOM ENVIRONMENT -A PRELIMINARY SOURCE INVENTORY AND BUDGET

This paper presents the first attempt to quantify the production, cycl ing, storage and loss of PAHs in the UK environment. Over 53000 tonnes of Sigma PAHs (sum of 12 individual compounds) are estimated to resid e in the contemporarly UK environment, with soil being the major repos itory. If soils at contaminated sites are included this estimate incre ases dramatically. Emission of PAHs to the UK atmosphere fi om primary combustion sources ale estimated to be greater than 1000 tonnes Sigma PAHs per annum, with over 95% coming from domestic coal combustion, u nregulated fires and vehicle emissions. It is estimated that approxima tely 210 tonnes of Sigma PAH are delivered to terrestrial surfaces eac h year via atmospheric deposition. Therefore, inputs of Sigma PAHs to the UK atmosphere outweigh the outputs by a factor of over 4. This may be explained by enhanced particulate deposition near point sources, P AH degradation in the atmosphere and transport away from the UK with p revailing winds. Disposal of waste residues is estimated to contribute a further 1000 tonnes of Sigma PAH per year to the terrestrial enviro nment. It is illustrated that the use of creosote has the potential to release considerable quantities of PAHs to the UK environment. Tempor al trends in PAH cycling are then considered. There is good evidence t o suggest that air concentrations and fluxes to the UK surface are now lower than at any time throughout this century. Nonetheless, the UK S igma PAH burden is still increasing at the present time, principally t hrough retention by soils. However, there are marked differences in th e behaviour of individual compounds: there is evidence, for example, t hat phenanthrene concentrations in soils have declined since the 1960s , although soil concentrations of benzo[a]pyrene and other heavier PAH s have continued to increase through this century. Volatilisation of l ow molecular weight PAHs accumulated in soils over previous decades ma y be making an important contribution to the current atmospheric burde n. The major uncertainties identified by data on this budget are: (1) the lack of PAH concentrations in some environmental matrices; (2) the possible importance of contaminated soils as a major repository and s ource of PAHs; (3) the lack of emission data (especially vapour phase releases) for some PAH sources; (4) the importance of biodegradation a nd volatilisation as loss mechanisms for low molecular weight PAHs in soils; and (5) the importance of creosote use in the PAH cycle.