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.

The N balance has been studied in detail in the basins of small rivers under agricultural management and forest use. The N content of the watershed territory of large forests was found to be practically balanced. In the river basin where the land was intensively farmed for 10 yr, N input increased five times through mineral fertilizers, and one-and-a-half times through organic fertilizers. Consequently, the amount of N returned to the atmosphere as a result of denitrification increased by one-and-a-half times, and that leached into the ground water, increased from 0.8 to 6.5 mg 1('-1) N.

Laboratory experiments were conducted to determine the effects of Kepone on the larval development of the mud-crab, Rhithropanopeus harrisii, and the commercial blue-crab, Callinectes sapidus, from the time of hatching until the 1st crab stage was reached. Differential survival of R. harrisii from hatching to 1st crab stage occurred in a range of 35 to 125 ppb Kepone, whereas differential survival of C. sapidus over the same period of development occurred in a range of 0.1 to 1.0 ppb. Statistical analysis indicated that, for every 10 ppb Kepone added, duration from hatching to 1st crab stage of R. harrisii was increased by 0.391+/-0.043 days; whereas for each increase of 0.1 ppb, the duration from hatching to 1st crab stage of C. sapidus is prolonged by 0.38+/-0.10 days. The 1st and 2nd zoeal stages of R. harrisii were the most sensitive developmental stages to Kepone, but the 1st zoeal stage of C. sapidus was not sensitive, statistically, to any concentration of Kepone tested. In zoeal stages II, III and IV, there were significant increases in mortality of C. sapidus over the previous stage in all media tested.

This analysis measures trade-offs between soil loss and food production costs. It is made by means of multigoal interregional programming model. The trade-off curve is derived by means of the prior weighing technique. The results indicate that soil loss from agricultural land can be decreased considerably with very little increase in cost in efficiency in food production. However, the trade-off curve has a "corner" in it, and further reductions in soil loss give rise to sharp increases in food production costs. As higher costs are assigned soil loss, important shifts take place in the interregional patterns of crop production and land use. Also, further decreases in soil loss and increases in food production costs raise food prices for consumers.

Eight plant species were subjected to artificial acid rains of pH 2.5, 2.0, 1.5, 1.0 and 0.5 in order to determine the threshold for and symptoms of damage. The plants were Erechtites, Robinia, Pinus, Quercus, Carya, Liriodendron, Acer and Cornus from the Coweeta Hydrologic Laboratory near Franklin, North Carolina. Droplets of pH 2.0 produced brown necrotic spots on all species except Pinus while droplets of pH 1.0 produced necroses on leaves of all species examined. The size of necrotic spots increased with increasing acidity. Comparison of these results with the literature suggests that developing leaves are more easily damaged than are the mature leaves used in this study. The volume weighted average rainfall pH for Coweeta is 4.6 with observations ranging from 3.2 to 5.9. Results of this study suggest that a 10-fold increase in acidity from pH 3.2 to 2.2 in a single spring or summer storm could bring damage or death to mature leaves of dominant flowering plants in the Southern Appalachians.