ELSEVIER PII: S0269-7491(97)00096-1 Environmental Pollution, Vol. 97, No. 3, pp. 229-238, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printvd in Crrcat Britain 0269-7491/97 $17.00+0.00 MEASURED AND PREDICTED VOLATILISATION FLUXES OF PCBS FROM CONTAMINATED SLUDGE-AMENDED SOILS Ian T. Cousins, Nicola Hartlieb, Claudia Teichmann and Kevin C. Jones* Environmental Science Division, Institute of Environmental and Biological Sciences, Lancaster University, Lancaster LA1 4 YQ, UK (Received 7 April 1997; accepted 30 June 1997) Abstract A laboratory experiment was carried out to measure volatilisation fluxes of polychlorinated biphenyls (PCBs) from sewage sludge-amended soils. The most commonly practised methods of applying sludge to agricultural land in the UK, namely, surface application, ploughing in to soil and subsurface injection, were simulated inside glass experimental chambers using an anaerobically digested sludge and a sandy loam soil. Humidified air was blown over the surface of the soil/sludge in the chambers for a period of 32 days, in order to sample a sufficient air volume to detect the volatilising PCBs. The resulting PCB volatilisation fluxes from the different sludge appli- cation methods were quantified and compared. Volatilisa- tion fluxes of individual congeners were generally highest for the surface sludge (1-cm depth) application and slightly lower for the plough layer (5-cm depth) applica- tion. Fluxes from the subsurface layer of sludge (5-cm depth) were only quantified for the lightest congeners near to the end of the experimental run-time. Results from a multiple regression analysis showed that volatilisation fluxes of PCBs from the surface application are highly dependent on both the sludge concentration and the log of the octanol-air partition coefficient (KoA). A well-known soil volatilisation model, developed by Jury et al., was adapted and used to predict fluxes for the different sludge application methods during the experiment. The model predicted volatilisation fluxes that were reasonably com- parable to measured fluxes for some congeners, but for others predicted fluxes that were more than an order of magnitude lower than measured fluxes. The model pre- dicted similar loss kinetics to those observed in the experiment. Possible reasons for the dissimilarity between measured and predicted fluxes include inaccuracies in model input parameters and the fact that the models were not developed for predicting fluxes from sludge-amended soils. © 1997 Elsevier Science Ltd INTRODUCTION In 1992 1.0x 106 tonnes (dry weight) of sewage sludge were produced within the United Kingdom (UK) *To whom correspondence should be addressed. Fax" +44 1524 593985; e-mail: k.c.jones@lancaster.ac.uk. 229 (RCEP, 1996). Spreading onto agricultural land is the commonest destination for sludge in the UK and in 1992 this was the fate of about 50% of the total sludge produced (RCEP, 1996). The amount spread on land is expected to almost double by the year 2005, because the amount of sludge produced is set to increase to 1.5 x 106 tonnes (dry weight) and because one of the current des- tinations for sludge in the UK, marine disposal, will be banned in the European Union in 1998 (RCEP, 1996). Polychlorinated biphenyls (PCBs) are just one of a wide range of organic contaminants that concentrate onto organic-rich particles during wastewater treatment and are found in the solid residue known as sewage sludge. The behaviour, fate and significance of organic contaminants in sludge have not received the same amount of attention as metals and no corresponding guidelines exist as yet in the UK to control the disposal of sludges contaminated with organics, although there has been some attempt to set standards for a limited number of compounds in a few other countries, e.g. for dioxins in Germany. There is increasing concern about the presence of certain organics in sludge, in particular regarding their application to agricultural land and movement through terrestrial food chains, because of the reported increased mutagenicity and persistence of some compounds, including PCBs, in soils amended with sludge (Duarte-Davidson and Jones, 1996; Wilson et al., 1996). Contemporary PCB concentrations in UK sewage sludges are generally less than 1 mg kg -1 (~PCB, dry weight), but were probably higher in the past (Alcock et al., 1993). PCBs have fairly low vapour pressures, but their low water solubility renders water to air transport an important mechanism with respect to their environ- mental distribution, as demonstrated by some of the Great Lake's research (e.g. Jeremiason et al., 1994). Soil to air transport has been shown to be an important loss process for PCBs from soils (Moza et al., 1979; Alcock et al., 1996) and this mechanism will have a marked influence on the global distribution of these compounds (Jones, 1994). The mechanisms involved in the soil to air transfer of PCBs will involve a combination of direct soil organic matter to gas-phase transfer and soil pore- water to air transfer. Despite the significance of soil-air transfer of PCBs and other persistent semi-volatile organic compounds (SOCs), there is still a paucity of