A field study was performed on the effects of acid mine leachate from slate mine tailings seeping into a small river passing through the tailings. Before entering the tailings the river water has high alkalinity which neutralizes acidity upon mixing with leachate within the tailings. Donwstreams of the tailings the pH of the river water ranges about pH = 8, the water contains high concentrations of sulfate (≈1500 μmol/1 and particulate bound aluminium (≈80 μmol/I), but low concentrations of dissolved aluminium (≈3 μmol/1). It is therefore assumed that AI(OH)₃ colloids are precipitated during the neutralisation process and transported out of the tailings. The concentration of particulate bound aluminium along the river shows a strong correlation with the concentration of sulfate, which indicates that particulate bound aluminium is conservative. It therefore seems that under dry weather conditions (under most of the sampling was performed) no chemical retention mechanism exists which confines the distribution of aluminium to a restricted part of the catchment area. In contrast, the white river sediment is rich in both aluminium and sulfate, which suggests the temporary formation of aluminium hydroxosulfate minerals. Favorable (i.e. acidic) conditions may prevail at high discharges where the acidity accumulated in the tailings is flushed into the river with its subsequent acidification.

Total mercury (Hg) and methylmercury (MeHg) concentrations were determined in sediments and in the polychaete wormNereis diversicolor at 13 stations of a brackish water intertidal mudflat of the Scheldt estuary. Hg and MeHg concentrations in sediments ranged from 144 to 1192 ng g⁻¹ dw and from 0.8 to 6 ng g⁻¹ dw, respectively. Both Hg and MeHg concentrations increased with an increase of organic matter (OM) content and fine grain fraction. In contrast, Hg accumulation byN. diversicolor was significantly (p<0.05) higher at stations with sandy sediments (mean value: 125 ng g⁻¹ dw) than at stations with muddy sediments (mean value, 80 ng g⁻¹), probably because Hg availability for bioaccumulation at muddy stations was reduced by high OM content of the muddy sediments. MeHg accounted for an average of 0.7% of the total Hg in sediments and 18% of the total Hg inN. diversicolor. Seasonal variations significantly affected Hg concentrations in sediments and MeHg inN. diversicolor. Total Hg concentrations in sediments were significantly (p<0.05) higher in autumn and winter than in spring and summer whereas MeHg concentrations were lowest in winter compared to the other seasons. On the other hand, total Hg concentrations in the worms were lowest in spring whereas MeHg concentrations were significantly (p<0.01) higher in spring and summer than in autumn and winter.

The effectiveness of ammonia stripping at different air flow rates (0, 1 and 5 L min⁻¹) and lime dosages (0 and 10 000 mg L⁻¹ calcium hydroxide) was investigated in aeration tanks in a laboratory as a pretreatment to remove ammoniacal-nitrogen and organic load (COD) in landfill leachate. Ammoniacal-nitrogen removal at 20 °C after one day was 70% for 0 L min⁻¹, 81% for 1 L min⁻¹ and 90% for 5 L min⁻¹ regardless of the origin of leachate. Ammonia loss was mainly due to desorption through water surface. The levels of phosphorus and COD were only reduced by lime precipitation, with 85% and 93% phosphorus removal and 24% and 47% COD removed for leachate from the Junk Bay Landfill (JB) and Gin Drinkers' Bay Landfill (GDB) respectively. The highly significant difference (P<0.05) of COD removal between JB and GDB might be due to the different age of the two landfills studied. Leachate quality and configuration of the treatment reactor were important factors affecting the efficiency of ammonia removal by stripping processes.

Increasing mercury contents are reported from freshwater systems and fish in northern Europe and North America. Mercury input from soils is a major source with the leaching being affected by increased atmospheric mercury deposition compared to pre-industrial times and by other environmental conditions such as acid rain. The results of a mathematical model-calculation of vertical inorganic Hg(II) leaching in a Scandinavian iron-humus podzol under different atmospheric input rates of mercury are presented. Leaching under background rain conditions was calculated to be considerably stronger than under acid rain conditions. Increasing fractions of deposited soluble or solute atmospheric mercury were leached from the Of₍ₕ₎-horizon with decreasing soil content of soluble mercury under acid rain conditions; this effect was less pronounced under background rain conditions. The steady state concentrations of soluble mercury of the upper soil horizons were calculated and compared with the actual concentrations of total (= soluble + insoluble mercury) and extractable (= estimate of soluble) mercury measured in these horizons. The results indicate that even if the deposition of airborne mercury to soil is strongly reduced, the total mercury content of the soil decreases only slowly. It may take decades or even centuries before a new steady state concentration of total mercury is established in the soil. The decrease of the mercury concentration in the Of₍ₕ₎-horizon is probably largely dependent on the turnover of organic matter, binding most of the deposited airborne mercury in an insoluble form. Hence, present day mercury leaching is likely to be dominated by mercury deposited during former times and temporarily retained in an insoluble form in the organic matter.

Combined effects of organic or inorganic pollutants on soil microbial activities were investigated in field plots grown with four types of covering plants. It was derived from this study that combined effects were dependent not only on the type and dose of pollutants, addition of soda lime, plant type and season variation, but also on test parameters. When jointly added, higher doses of Cd, Cu, Pb, Zn and As caused significant inhibition. Addition of soda lime could even enhance inhibition. Joint effects of phenanthrene, MET (active ingredient: paclobutrazol) and 1,2,4-trichlorobenzene were not significant, and may be covered by other biotic or abiotic factors. Compared with other two parameters (respiration and microbial biomass), dehydrogenase activity appeared to be more sensitive for evaluating the toxicity of anthropogenic pollutants in soil. Soil samples collected in summer often had higher microbial activities than those in fall. The microbial activity in soil decreased with covering vegetation in the order alfalfa > pine > poplar and maize, albeit some exceptions were observed.

The concentrations of As, Br and I were measured in needles, in the material deposited on the needle surface and in the soil. Results from 8 unpolluted and one polluted continental sites and from one maritime site are reported. The mass of al13 elements on the needle surface is similar to that in the needles. Needle concentrations increase linearly with the needle age class, but net accumulation during the first year is larger than during later years. There are significant correlations between the material on the needle surface and the needle concentrations for As and Br, but not between the soil and the needle concentrations. Bromine values are much higher at the polluted and at the maritime site than at the unpolluted sites.

In view of the toxic nature of Beryllium and its compounds the disposal of waste materials containing beryllium needs prior evaluation. The present study was undertaken to obtain information on the leachability and immobilisation of beryllium from solid waste red-mud generated in processing Beryl at the Beryllium Metal Plant at Vashi, New Bombay. The studies showed that 62% of the total beryllium in red-mud can be extracted by water by repeated leaching over a period of 445 d. The mixing of the waste material with cement and casting into cement blocks reduced the leachability of beryllium to 0.11% which got further reduced to 0.02% by thermal curing of cement blocks.