Effects of the phenylurea herbicide isoproturon on periphytic diatom communities in freshwater indoor microcosms

The toxic effects of the phenylurea herbicide Isoproturon -IPU: (3-(4-isopropylphenyl)-1, 1-dimethylurea)-were studied on the colonization of periphytic diatom communities, within indoor microcosms consisting of a mixed biotope (water column and natural sediment) and two biological species-rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea). The periphyton, essentially composed of diatoms, was collected on artificial substrata (glass slides) in the upper layers of the water column, after two periods of exposure (34 and 71 days). IPU was initially added in the water or in the sediment compartment, at two nominal concentrations (L1 and L2 levels) for each contamination source-5 and 20 microg litre(-1) and 100 and 400 microg kg(-1) in sediment (w/w) respectively. The effects of IPU on the density and community structure of periphytic diatoms are described. A marked reduction in the diatom density was observed after 34 days exposure to the lower concentration of IPU in the water (5 microg litre(-1)). For the L2 levels, the very small number of live cells present did not permit quantification of the diatom density. After 71 days, recovery in community parameters occurred for the two contamination levels of the sediment and water column sources. Samples collected in the experimental units contaminated with the L2 levels were dominated by heterotrophic and smaller diatom species, such as Sellaphora seminulum. Data treatment based on factorial discriminant analysis enabled us to distinguish the different contamination conditions, with only 11 species from the 130 taxa identified.     

Induction of aryl hydrocarbon hydroxylase by chlorinated dibenzofurans in rats

Five of 25 chlorinated dibenzofurans induced aryl hydrocarbon hydroxylase in rats when administered orally at 40 μg/kg body weight. Active inducers included the three congeners with chlorines in all four lateral positions and the 2,7- and 2,8-dichlorodibenzofurans. The findings agree well with other studies involving common congeners, but do not agree with findings in that congeners with three lateral chlorines were inactive .     

Effects of elevated CO2 concentration on the polyamine levels of field-grown soybean at three O3 regimes

Effects of increased ozone (O3) and carbon dioxide (CO2) on polyamine levels were determined in soybean (Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre(-1) O3 and CO2 treatments equal to 350, 400 and 500 microl litre(-1) for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO2 ameliorated the deleterious effects of increased O3. Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O3 at ambient CO2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO2. Elevated CO2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O3-induced increases in Put and Spd at ambient CO2 concentrations. However, increased CO2 levels inhibited this response by blocking the O3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O3 or CO2 effects on polyamine levels. Our results demonstrate that current ambient O3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO2 to protect soybeans from O3 damage, however, does not appear to involve polyamine accumulation.     

Neurotoxicology of ortho-substituted polychlorinated biphenyls

Ortho-substituted, non-planar PCBs reduce dopamine content in both nonhuman primate brain and pheochromocytoma (PC12) cells. Planar, dioxin-like, congeners have no effect on dopamine content in PC12 cells. Additional in-vitro results indicate that dopamine reduction by PCBs is due to inhibition of tyrosine hydroxylase activity.     

Field studies of ethoprop movement and degradation in two Florida soils

Unsaturated- and saturated-zone field studies were conducted under two different agricultural conditions in Florida, U.S.A., to measure the movement and degradation of ethoprop.When ethoprop was applied to a sand soil in an orange grove located on the Florida central ridge, soil residues declined with a half-life of 13 days to near the limit of detection (0.01 μg g⁻¹ within 2 months. Ethoprop residues were generally contained in the upper 2 m of soil. Although low levels of ethoprop were found in four groundwater samples within the first 3 months after application, the cause of these isolated and transient residues could not be determined. The data show that there was no widespread plume of ethoprop residues beneath or downgradient from the treated area.On a flatwood soil on the west coast of Florida, ethoprop was incorporated into raised beds and protected by a plastic mulch in which tomatoes were grown. When the plastic mulch was present, ethoprop soil residues declined with a half-life of 40 days and were confined to the upper 0.3 m of soil. After the mulch was removed at crop harvest, the remaining ethoprop dissipated with a half-life of 12 days. Groundwater residues in excess of 1 μg L⁻¹ were confined to a single sample collected after the well had been damaged during a rototilling operation. Resides of < 1 μg L⁻¹ were present in three later samples from this well. At the sampling interval where the highest residues were detected in the damaged well, ethoprop residues of < 1 μg L⁻¹ were also found in three other wells but no residues were detected in these wells in later samples.     

Environmental hazard profile of organic chemicals: An experimental method for the assessment of the behaviour of organic chemicals in the ecosphere by means of simple laboratory tests with 14C labelled chemicals

The concept of “Environmental Hazard Profile” developed at this institute has been tested with 100 ¹⁴C-labelled organic compounds. Concentration factors in activated sludge, in algae and fish were determined. The microbial degradation of the chemicals to CO₂ in activated sludge and the decomposition to CO₂ under artificial light were determined. Ranking of compounds is given in the order of falling concentration factors and accumulation in rats respectively, and decreasing rates of decomposition. Relationship between chemical structure and accumulative and degradative behaviours is demonstrated using some selected groups of chemicals, such as benzenes, phenols, biphenyls and polyaromatic hydrocarbons. Correlations between the octanol/water partition coefficient, concentration factors and rates of decomposition could be established. Evaluation of test compounds was possible using hazard profiles obtained by the sum of single test results.