Salem S. Rao

Cohesive sediment transport: emerging issues for toxic chemical management

The association of many environmentally sensitive chemicals and their transformation products with mineral and organic substrates is of considerable importance for environmental monitoring, prediction and management purposes in rivers and their basins. Our understanding of these relationships is poor. This paper reviews processes of particular concern, including the physical behaviour of fine-grained (< 63 µm) sediment in freshwater; the role of flocculation as a transport vector; the processes that control freshwater flocculation including microbiological factors; the uncertainty in conventional sediment transport models for predicting pathways of sediment-associated chemistry; the relationship between suspended sediment and toxicity in the water column; and the partitioning of chemicals between the sediment, organic and water phase, including the significance of these in predicting chemical transport on suspended matter.

Influence of acid precipitation on bacterial populations in lakes

Relative abundance of total, respiring, aerobic heterotrophic, nitrogen cycle and sulfur cycle bacteria was measured in acid stressed and non-acid stressed hard water lakes. Data indicated that bacterial populations and densities were nearly an order of magnitude less in acid stressed waters than in non-acid stressed waters. Nitrifying bacteria and some sulfur cycle bacteria (Thiobacillus sp.) were very low or absent in acid stressed waters. Surface sediments of acid stressed lakes contained 3 to 4 times more organic matter than the amount found in the relatively more enriched lake. Methodology and data are presented.

Mutagenicity and toxicity assessment of pulp mill effluent

Data are presented on the mutagenic and toxic properties of both whole and fractionated bleached kraft mill effluent. Mutagenic properties were measured using the Ames test and the SOS Chromotest. Toxic properties were measured using the Microtox and Daphnia magna bioassays. The D. magna bioassays were performed only on four samples, and the information on mutagenicity represent the main emphasis of this study. Various fractionation procedures, including filtration, centrifugation and XAD resin adsorption procedures were employed. Bleached kraft mill effluent (BKME) was found to be mutagenic with the majority of activity associated with polar compounds. Polar material adsorbed by XAD-4 and XAD-8 resins contained a mutagenic potency equivalent to that measured directly in the effluent. Whole effluent samples were non-toxic (Microtox bioassay), but the polar fractions were toxic (Microtox and Daphnia magna bioassays) while particulate associated materials were toxic just to the Microtox bioassay. This paper also comments on the chemical characteristics of mutagenetic materials in these effluent fractions.

Response of lake sediments to changes in trace metal emission from the smelters at Sudbury, Ontario.

Historical records preserved in sediments show that the lakes are extremely sensitive to metal emissions from the smelters in the Sudbury basin. From the observed quick response, a strong capacity for rapid recovery (deacidification) of acid-stressed lakes in the area is deduced. The study thus emphasises the need for curtailing the emissions of acidic and acidifying substances as a critical step in reducing lake acidification as well as in rehabilitating many of the afflicted lakes.

Effects of low-pH stress on the morphology and activity of bacteria from lakes receiving acid precipitation

Field and laboratory studies on the effects of low-pH stress are reported here for lacustrine bacteria. Two biochemical parameters, respiration and substrate utilization, reveal a marked decrease under severe low-pH stress. Bacterial ultrastructure and cell diversity can be correlated with a given level of pH. Structural changes in the cell envelope as a function of pH are highlighted. The biochemical, physiological and morphological observations are united into a hypothesis which seeks to relate cell adaptation to environmental stress.

Assessment of the genotoxic potential of pulp mill effluent using bacterial, fish and mammalian assays

Abstract Extracts of bleached kraft mill effluent (BKME) have been shown to contain mutagenic activity and to induce biochemical responses in fish, such as increased activity of the mixed-function oxygenase (MFO) enzyme system. Recent work has shown that Ames-positive substances in BKME are direct-acting mutagens, and that the majority of mutagenic activity is extracted by XAD-4 and XAD-8 resins and eluted by aqueous solutions of sodium hydroxide (NaOH) or methanol (MeOH). In this study, the genotoxic potency of BKME extracts was further assessed using a bacterial (Umu-C) genotoxicity assay, an in vivo hepatic micronucleus assay with trout, and an in vitro assay for DNA strand breaks with Chinese hamster lung V79 cells and two mouse liver cell lines (TIB 73 and TIB 75). The majority of mutagenic substances from the filtered effluent were adsorbed by XAD-4 and XAD-8 resins and DEAF cellulose, and were effectively removed from these adsorbents by NaOH or McOH. The mutagenic fraction extracted by XAD-4 and eluted by McOH consistently induced DNA strand breaks in the assays with V79, TIB 73, and TIB 75 cells. Activity of these fractions was not altered by the addition of rat liver microsomes or dialysed liver cytosol from various vertebrate species. The fractions extracted by XAD-8 and eluted with NaOH, and extracted by XAD-8 and eluted with McOH did not induce DNA damage in assays with V79 cells. The genotoxic responses indicated direct acting genotoxicity to mammalian and fish cells and correlates with bacterial mutagenicity, and that these bioassays are complementary when applied to screening of BKME samples for genotoxic potential.

Fish hepatic micronuclei as an indication of exposure to genotoxic environmental contaminants

An In vivo assay protocol for detecting hepatic micronuclei in fish was performed to evaluate whether this genotoxic response could serve as a bioindicator of environmental exposure to genotoxic substances. The incidence of hepatic micronuclei was compared in brown bullheads (Ameiurus nebulosus) with external lesions collected from a contaminated site and fish showing no externally visible pathologies collected from reference sites. Laboratory experiments were performed by exposing hatchery-raised rainbow trout (Onchorhynchus mykiss) to a pulp mill effluent extract (XAD-4-NaOH) with known genotoxic activity. Both bullhead and trout were injected with allyl formate to induce hepatic necrosis and regenerative proliferation of hepatocytes prior to examining the liver tissue for micronuclei. An elevated incidence of hepatic micronuclei was observed in Hamilton Harbour bullheads showing visible lesions relative to the micronucleus incidence in bullheads from reference sites with no external pathologies. Similarly, rainbow trout exposed to pulp mill effluent extracts exhibited an elevated incidence of hepatic micronuclei compared to controls. These results suggest that the hepatic micronucleus assay could serve as a valuable biomonitoring tool for assessing the impacts of genotoxic environmental contaminants on fish. ©1997 by John Wiley & Sons, Inc. Environ Toxicol Water Qual 12: 217–222, 1997

River evaluation using ecotoxicological and microbiological procedures

One of the many problems researchers and managers face is to try and interpret data collected from various river studies. There is an underlying awareness of the incompleteness of most data bases due to a variety of problems outside of those concerning sample processing.In this study we have attempted, by using the battery of tests approach (12 tests) and the examination of different types of samples such as water, Milli-Q water extracted sediments, and organic solvent extracted sediments, to explore the implication of spacial and temporal sampling programmes.The results obtained were not unexpected: there were spatial and temporal influences, sometimes so great that it would appear that you were examining samples from different parts of the country. However, data arising from solvent extracted sediments were found to be much less influenced by temporal sampling than by spatial variation. Another interesting and important observation was that sediment composition appeared to have no relationship to toxicant content.In this study, the first field application of the Mutatox test (genotoxicity) was carried out and it was found to be a very responsive test in all three types of samples. This test shows great promise as laboratory studies indicate it is sensitive to many of the chemicals which trigger the Ames test.

Downcore sulphur isotope ratios and diatom inferred pH in an artificially acidified Canadian shield lake.

Three gravity cores were removed from near the deepest point in Lake 223 on 9 June 1984, eight years after the Experimental Lakes Area (ELA) staff began the artificial acidification of the lake with sulphuric acid. The first of these cores was analysed for diatoms and pollen stratigraphy while the second and third were analysed for downcore sulphur isotope ratios (H. Thode) and downcore changes in sulphur reducing bacterial densities (S. Rao). Sediment core chronologies were based on lead-210 and cesium-137 data (R. Anderson) and the Ambrosia pollen rise (M. Dickman). Analysis of the first core to the depth of the Ambrosia pollen rise (9 cm) indicated that diatom inferred pH in Lake 223 at the time of the Ambrosia rise (circa 1890) was 6.8-7.0. At a sediment depth of 3 cm the diatom inferred pH was 6.7. Thereafter diatom inferred pH began a decline culminating in the present day (observed) pH range for 1984 (5.3-5.5). At a sediment depth of 1 cm, an increase in the abundance of two benthic alkalophilic diatoms occurred. The increase in the abundance of these diatoms was ascribed to an increase in hypolimnetic alkalinity following the artificial acidification of Lake 223. This is the first time that lake acidification has been linked to an increase in benthic alkalophilic diatoms associated with hypolimnetic alkalinity production following sulphate reduction. Sulphur in the anaerobic (black) sediment layers (0-1.5 cm) was isotopically light relative to the sulphur in the deeper layers. This was due to sulphur isotope fractionation resulting from the bacterial reduction of sulphate to hydrogen sulphide in the anaerobic portion of the water column. A jet black FeS-rich layer in the uppermost 1.5 cm of the lakes sediments was associated with an increase in the abundance of sulphate reducing bacteria (e.g. Desulfovibrio spp.).

Acid stress and lake bacteria: Ultrastructural and physiological correlates of some acid and copper stresses

A description is given of concurrent changes in bacterial ultrastructure and physiology in relation to applied stresses of acid and/or copper: the environmentally-relevant correlations are explored as a potential tool for ascertaining mechanisms of acid rain damage. Ultrastructural analysis permits a differentiation, on a gross scale, between different levels of acid and combined acid/copper stresses in laboratory experiments on enrichment cultures of lacustrine microbial populations rich in Gram-negative bacteria. For the dominant morphotypes of Gram-negative bacteria, changes in the cell envelope (and its extensions) correlate also with changes in activity of envelope-associated enzymes.