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.

Certain blood morphology parameters: red blood cell (RBC) sizes; percentage of polymorphonuclear leukocytes and ratio polychromatocyte/RBC in Brown trout (Salmo trutta L.) from acidified water (mean pH value 4.94) and limed water (mean pH value 5.66) were investigated. The sizes of RBC long axises were significantly larger in fish from acidic environment than from limed condition (14.37 and 12.96μm respectively). The percentage of polymorphonuclear cells (7.86 and 3.32) and polychromatocyte/RBC ratio (0.079 and 0.019) were also significantly larger in fish from the acidified environment. Blood morphology parameters are concluded to be usefull for testing and detection of long-term acidic stress in fish in nature.

The measurement and induction of mixed function oxyigenases (MFOs) of limnetic gastropods were investigated to estimate their suitability as biomarkers. A determination of MFO activities was performed through the measurement of ethoxyresorufin-O-dealkylase (EROD), pentoxy-(PROD) and benzoxyresorufin-O-dealkylase-activity (BROD). Optimal measuring conditions of these activities were investigated in preparations of the digestive gland of 4 species of limnetic gastropods. Results indicate that MFO-activity inhibiting substances are accumulating in the microsomal pellet, the fraction commonly used for the measurement of MFO-activities. Therefore, the fraction used for induction studies was the postmitochondrial supernatant (PMS). EROD, PROD, and BROD activity ofPlanorbis planorbis andPlanorbis carinatus were measured after a treatment with Aroclor 1254 for 1–17 days. Maximal induction of EROD and PROD were 6 and 10 times the value in the control group ofP. carinatus, respectively induction inP. planorbis was lower. BROD-activity could not been measured inP. planorbis. InP. carinatus, BROD-activity increased to a maximum of 2 times after traetment with Aroclor 1254. The level of induction of EROD-activity is comparable to results described in analog studies with fish.

Substituted phenols, anilines, pyridines and mononitrobenzenes can be classified as polar narcotics. These chemicals differ from non-polar narcotic compounds not only in their toxic potency (normalized by log Kₒw), but also in their Fish Acute Toxicity Syndrome profiles, together suggesting a different mode of action.For 97 polar narcotics, which are not ionized under physiological conditions, 11 physico-chemical and quantum-chemical descriptors were calculated. Using principal component analysis, 91 % of the total variance in this descriptor space could be explained by three principal components which were subsequently used as factors in a statistical design. Eleven compounds were selected based on a two-level full factorial design including three compounds near the center of the chemical domain (a 2³+3 design).QSARs were developed for both the design set and the whole set of 63 polar narcotics for which guppy and/or fathead minnow data were available in the literature. Both QSARs, based on partial least squares regression (3 latent variables), resulted in good models (R²=0.96 and Q²=0.82; R²=0.86 and Q²=0.83 respectively) and provided similar pseudo-regression coefficients. In addition, the model based on the design chemicals was able to predict the toxicity of the 63 compounds (R² =0.85).Models show that acute fish toxicity is determined by hydrophobicity, HOMO-LUMO energy gap and hydrogen-bond acceptor capacity.