Abstract. Samples of forty sewage sludges taken in England during 1979 were analysed for ten heavy metals using a rapid flameless atomic absorption spectroscopic technique. For all metals the mean concentrations were influenced by a small number of sludges containing exceptionally high concentrations. Typically, the concentration ranges showed approximately a 100-fold spread. Calculations based on U.K. guidelines for limiting the addition of toxic metals in sludge to agricultural soils indicated that application rates would theoretically be limited for more than 75% of the sludges by the concentrations of Zn, Cu and Ni, expressed additively as the Zn equivalent. Calculations of the theoretical maximum quantities of sludges which could be applied to land on an annual basis suggested that a significant proportion of the sludges would be unsuitable for application to agricultural land at rates of more than 2 t ha('-1) yr('-1).

The absorption and loss of tritiated water (HTO) vapor at bare soil and grass surfaces were studied in laboratory and field experiments. The exchange involves turbulent mixing in the air and diffusion within the soil. In short exposures it was found that uptake by moist soil was controlled by atmospheric mixing and was described by an exchange velocity of about 1 cm/s('-1). The exchange velocity was a little smaller for air-dried soil and grass surfaces. For exposure times exceeding a few minutes re-evaporation reduced the rate of net uptake, but the total amount deposited continued to increase as the HTO diffused deeper into the surface. The diffusion coefficient for HTO in soil was investigated in the laboratory and a simple equation was derived to predict the effective diffusion coefficient. Tritiated water, absorbed during a brief exposure, evaporated during several weeks. Its behaviour was described by the diffusion equation, but unexplained discrepancies were found in apparent diffusion coefficients in field conditions. Rain washed the activity into the soil and impeded evaporation. Most of the HTO vapor interacts with the surface within two or three days following a low level release. The effect of the surface exchange on the distribution of dose following a release of HTO vapor may be large, but will depend on the weather over a period of weeks and is difficult to foresee

Plant responses to air pollution were found to vary with type of leaf vesture. Considerable reduction in leaf area, leaf biomass, total plant biomass and chlorophyll content was observed in plants having pilose or pubescent leaf surface as compared to plants with glabrescent leaf surface. The study shows the importance of leaf vesture in determining response of plants to air pollution.