Acute toxicity of zinc and arsenic to the warmwater aquatic oligochaete <Emphasis Type="Italic">Branchiura sowerbyi</Emphasis> as compared to its coldwater counterpart <Emphasis Type="Italic">Tubifex tubifex</Emphasis> (Annelida,Clitellata)

Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

     

Biochemical parameters in Tubifex tubifex as an integral part of complex sediment toxicity assessment

Background, aim, and scope

Restoration of lakes and reservoirs with extensive cyanobacterial water bloom often requires evaluation of the sediment quality. Next to the chemical analysis of known pollutants, sediment bioassays should be employed to assess toxicity of the present contaminants and to make predictions of associated risk. Brno reservoir in the Czech Republic is a typical example of water bodies with long-term problems concerning cyanobacterial water blooms. Comprehensive assessment of reservoir sediment quality was conducted since successful reservoir restoration might require sediment removal. An important part of this survey focused on an examination of the utility of Tubifex tubifex and its sublethal biochemical markers for the assessment of direct sediment toxicity.

Materials and methods

This complex study included chemical analysis of contaminants (heavy metals, organic pollutants), ecotoxicity testing of sediment elutriates (tests with Daphnia magna, Pseudomonas putida, Sinapis alba, Scenedesmus subspicatus), and other parameters. We have tested in more detail the applicability of T. tubifex as a test organism for direct evaluation of contact sediment toxicity. Survival tests after 14 days of exposure were complemented by an assessment of parameters serving as biomarkers for sublethal effects [such as total glutathione content (GSH), activities of the enzymes glutathione transferase (GST), glutathione peroxidase (GPx), and glutathione reductase (GR)]. The data matrix was subjected to multivariate analysis to interpret relationships between different parameters and possible differences among locations.

Results

The multivariate statistical techniques helped to clearly identify the more contaminated upstream sites and separate them from the less contaminated and reference samples. The data document closer relationships of the detected sediment contamination with results of direct sediment exposure in the T. tubifex test regarding mortality but namely regarding the sublethal endpoints rather than the results obtained with other test organisms exposed to sediment elutriates. Aside from the reduction in T. tubifex survival, the sediments with organic pollution caused an increase in glutathione content and increased activities of glutathione S-transferase and glutathione peroxidase in the exposed T. tubifex worms.

Discussion

Results of our study confirm the suitability of T. tubifex for toxicity testing of raw waters and sediments. This longer-lasting direct contact test has proven more sensitive and appropriate to reflect a lower level of pollution than do the elutriate tests. Sensitive biochemical changes in T. tubifex, including an elevation in GSH levels and GST activities, reflect a general stimulation of detoxification metabolisms in the presence of xenobiotics. The results also suggest an important role of glutathione and related enzymes in detoxification processes and possible involvement of oxidative stress in toxicity mechanisms in benthic sediment-dwelling worms such as T. tubifex.

Conclusions

The complex assessment has identified the more contaminated samples with locally increased concentration of organic pollutants and significant ecotoxicity. The direct sediment contact test with T. tubifex and especially the biochemical parameters corresponded better to the lower level of pollution than the other tests with sediment elutriates. Despite its greater time and cost demands, the direct sediment contact test can provide a more realistic picture of exposure.

Recommendations and perspectives

Sediment bioassays should always be included as an integral part of the sediment quality assessment. The direct contact tests also take into account the more hydrophobic pollutants that are not easily available for the water elution but can still be accessible to the organisms. The T. tubifex test is a suitable option for contact sediment toxicity tests also because these animals show measurable sublethal biochemical changes that can be associated with this exposure.     

Effects of cadmium,mercury and lead on the survival and instantaneous rate of increase of Paronychiurus kimi (Lee) (Collembola)

The invertebrate springtail species Paronychiurus kimi (Lee) was selected for use in toxicity testing because it is more ecologically relevant to Korean soils than Folsomia candida Willem, which is the standard animal for toxicity tests. Responses of P. kimi to cadmium, mercury and lead were evaluated in artificial soils following the standardized ISO protocol. Although, reproduction of P. kimi was not as high as that of F. candida, 30 adults produced at least 200 juveniles over 28 days. For each of the three heavy metals, LC₅₀ and EC₅₀ for reproduction and NOEC and LOEC for the effect on reproduction and instantaneous rate of population increase (r_i) were also estimated. The 7 days LC₅₀ was 532, 3.9 and 1322 mg/kg dry soil for cadmium, mercury and lead, respectively. As exposure time increased from 7 to 28 days, the LC₅₀ values decreased for cadmium but not or only slightly for mercury and lead. The 28 days EC₅₀ was 60.0 for cadmium, 0.23 for mercury and 428 mg/kg for lead. Significant changes in r_i of P. kimi were closely followed by the changes in the sublethal endpoint measured (reproduction) and populations were heading toward extinction (r_i = 0) at concentration of 129, 2.0 and 1312 mg/kg dry soil for cadmium, mercury and lead, respectively. P. kimi was found to be more sensitive to all heavy metals tested than F. candida, confirming its suitability as a bioindicator species for soil toxicological testing in Korea.     

The Influence of Water Hardness, pH, and Suspended Solids on Nickel Toxicity to Larval Fathead Minnows (Pimephales promelas)

Nickel (Ni) is an ubiquitous, naturally occurring metalthat is associated with metal mining and other industrialactivities. Despite elevated Ni concentrations reportedfor many industrial receiving waters, Ni receives littleresearch attention addressing factors influencing itstoxicity to freshwater fish. This study examined theinfluence of water hardness, pH, and total suspended solids(TSS) in soft, reconstituted water on Ni toxicity to larvalfathead minnows (Pimephales promelas). Increasingwater hardness from 20 to 140 mg L^-1 (as CaCO₃) reduced acute Ni toxicity by 5-fold (96-h LC50s 0.45 and 2.27 mg Ni L^-1, respectively). Low pH had a slight protective effect against Ni toxicity relative to neutral pH conditions. At pH 5.5, the 96-h LC50 was 0.69 mg Ni L^-1, compared to 0.54 mg Ni L^-1 at pH 7.0. However,Ni toxicity was significantly reduced at pH 8.5 where the 96-h LC50 was 2.21 mg Ni L^-1. These results were explainedon the basis of Ni speciation. Total suspended solids also reduced Ni toxicity (expressed as 96-h LC50s) from 0.35 to 1.12 mg Ni L^-1 over a TSS range of 10 to 100 mg L^-1.This reduction of toxicity due to TSS is significant becausemine effluents often have a combination of elevated TSS andmetals. The ameliorative effect of TSS was not as significantas high hardness or pH probably because there is a TSS threshold, after which physical irritation to fish gills counteracts any protective effect conferred by TSS. This finding is relevant to choices made in design of mine effluenttreatment systems; i.e., there may be an optimum range ofTSS concentrations that protect aquatic biota againsteffects of metals that remain after treatment.     

Incubating Rainbow Trout in Soft Water Increased Their Later Sensitivity to Cadmium and Zinc

Water hardness is well known to affect the toxicity of some metals; however, reports on the influence of hardness during incubation or acclimation on later toxicity to metals have been conflicting. We incubated rainbow trout (Oncorhynchus mykiss) near the confluence of two streams, one with soft water and one with very-soft water (average incubation hardnesses of about 21 and 11 mg/L as CaCO₃, respectively). After developing to the swim-up stage, the fish were exposed for 96-h to a mixture of cadmium (Cd) and zinc (Zn) in water with a hardness of 27 mg/L as CaCO₃. The fish incubated in the higher hardness water were about two times more resistant than the fish incubated in the extremely soft water. This difference was similar or greater than the difference that would have been predicted by criteria hardness equations had the fish been tested in the different acclimation waters. We think it is plausible that the energy demands for fish to maintain homeostasis in the lower hardness water make the fish more sensitive to metals that inhibit ionoregulation such as Cd and Zn. We suggest that if important decisions were to be based upon test results, assumptions of adequate hardness acclimation should be carefully considered and short acclimation periods avoided. If practical, incubating rainbow trout in the control waters to be tested may reduce uncertainties in the possible influences of differing rearing water hardness on the test results.     

Toxicity (EC50) comparisons of some animal wastes

Toxicity of various animal wastes, after mixing with deionized water, for 1 and 24 hr, was measured using Photobacterium phosphoreum. The EC₅₀ values determined by the ‘microtox’ toxicity test showed that the aqueous extracts of all animal wastes were toxic and the toxicity increased in the order: cattle, horse, sheep, pig and poultry. The observed toxicity was found not to be influenced by the amount of kjeldahl-N, NO₃ or NH₄ present in the waste-extract.     

Cu and Ni Mobility and Bioavailability in Sequentially Conditioned Soils

The potential ecological hazard of metals in soils may be measured directly using a combination of chemical and biological techniques or estimated using appropriate ecological models. Terrestrial ecotoxicity testing has gained scientific credibility and growing regulatory interest; however, toxicity of metals has often been tested in freshly amended soils. Such an approach may lead to derivation of erroneous toxicity values (EC₅₀) and thresholds. In this study, the impact of metal amendments on soil ecotoxicity testing within a context of ion competition was investigated. Four coarse-textured soils were amended with copper (Cu) and nickel (Ni), incubated for 16 weeks and conditioned by a series of total pore water replacements. Rhizon^TM extracted pore water Cu, Ni, pH and dissolved organic carbon (DOC) concentrations were measured after each replacement. Changes in ecotoxicity of soil solutions were also monitored using a lux-based biosensor (Escherichia coli HB101 pUCD607) and linked to variations in soil solution metal and DOC concentrations, pH and selected characteristics of the experimental soils (exchangeable calcium (Ca) and magnesium (Mg)). Prior to conditioning of soils, strong proton competition produced relatively high EC₅₀ values (low toxicity) for both, Cu and Ni. The successive replacement of pore waters lead to a decline of labile pools of metals, DOC and alleviated the ecotoxicological protective effect of amendment impacted soil solution chemistry. Consequently, derived ecotoxicity values and toxicity thresholds were more reflective of genuine environmental conditions and the relationships observed more consistent with trends reported in historically contaminated soils.     

Zirconium toxicity assessment using bacteria,algae and fish assays

Our contribution to Zr environmental hazard, arrived at by means of bioassays on bacteria, microscopic algae and fish, confirms the hypothesis that Zr has low toxicity. Toxic effects revealed with the Microtox test may be attributed to pH rather than specifically to Zr (5 min. EC₅₀ > 4.3 mg L^?1). Fish assays also confirmed the low toxicity of Zr (96-hr LC₅₀ > 20 mg L^?1; 96 hr minimal stress concentration > 20 mg L^?1; Mutagenicity (Fluctuation test) and genotoxicity (S.O.S. Chromotest) assays failed to show any DNA-related effects linked to this metal. Only the algal assays (ATP energy stress) demonstrated genuine toxicity at Zr concentrations between 1.3 and 2.5 mg L^?1.     

Effects of Single Metals and their Mixtures on Selected Enzymes of Carcinus Maenas

In this work, the acute effects of copper, chromium and mixtures of both metals on females of the marine crab Carcinus maenas were investigated. The parameters indicative of toxicity were mortality and the activity of the enzymes acetylcholinesterase (AChE), lactate dehydrogenase (LDH) and glutathione-S-tranferases (GST). LC50 values determined at 96 hr were 51.8 mg L^-1 for copper, 49.8 mg L^-1 for chromium and 15 mg L^-1 Cu + 43.6 mg L^-1 Cr for the mixture of both metals. Copper, chromium and the mixtures of both metals significantly inhibit haemolymph AChE, ovarian LDH and hepatopancreas GST after an in vivo exposure of 96 hr to concentrations lower than NOEC values for mortality. Furthermore, the mixtures tested showed a more pronounced effect than individual agents.     

Attempts to derive EC50 values for heavy metals from land-applied Cu-, Ni-, and Zn-spiked sewage sludge

We established a field trial to assess the impacts on soil biological properties of application of heavy metal-spiked sewage sludge, with the aim of determining toxicity threshold concentrations of heavy metals in soil. Plots were treated with sludges containing increasing concentrations of Cu, Ni and Zn in order to raise the metal concentrations in the soil by 0-200 mg Cu kg⁻¹, 0-60 mg Ni kg⁻¹ and 0-400 mg Zn kg⁻¹, and were then cultivated and sown in ryegrass-clover pasture and monitored annually for 6 years. All biological properties measured (soil basal respiration, microbial biomass C, and sulphatase enzyme activities), except phosphatase activity, increased in all plots over the duration of the experiment. Consequently, it was only possible to assess effects of heavy metals across time if, each year, all data for each metal were normalised by expressing them as percentages of the activities measured in an un-sludged control plot. When this was done, no significant effects of increasing heavy-metal concentrations on basal respiration, microbial biomass C or respiratory quotient (qCO₂) were observed, although total Cu and soil solution Cu were significantly negatively related to microbial biomass C when it was expressed as a proportion of soil total C. None of the properties measured were affected by increasing Ni concentrations. Phosphatase and sulphatase activities were significantly negatively related to increasing Zn concentrations, but not usually to increasing Cu unless they were expressed as a proportion of total C. A sigmoidal dose-response model was used to calculate EC₂₀ and EC₅₀ values using the normalised data, but generally, the model parameters had very large 95% confidence intervals and/or the fits to the model had small R² values. The factors primarily responsible for confounding these results were site and sample variations not accounted for by the normalisation process and the absence of any data points at metal concentrations beyond the calculated EC₅₀ values. In the few instances where reasonable EC₂₀ values could be calculated, they were relatively consistent across properties, e.g., EC₂₀ for total Zn and phosphatase (330 mg kg⁻¹), total Zn and sulphatase (310 mg kg⁻¹), and EC₂₀ for total Cu and sulphatase (140 mg kg⁻¹) and total Cu and microbial biomass C (140 mg kg⁻¹), when both sulphatase and microbial biomass C were expressed as a proportion of total C. Our results suggest that Cu and Zn at the upper concentrations used in this experiment were possibly having adverse effects on some soil biological properties. However, much higher metal concentrations will be needed to accurately calculate EC₂₀ and EC₅₀ and this may not be easily achievable without many applications of sewage sludge, even if the sludge is spiked with heavy metals.     

Ecotoxicity of mercury to Eisenia fetida, Enchytraeus albidus and Folsomia candida

Despite growing concerns about the potential adverse effects of elevated mercury concentrations in the environment, only a few toxicity data are available for soil invertebrates. The chronic toxicity of mercury (II) was therefore assessed for Eisenia fetida, Enchytraeus albidus and Folsomia candida using standard test protocols. The 21-day EC₅₀ (the concentration causing 50% effect) for the cocoon production of E. fetida was 9.16 mg Hg kg^-1 dry wt. Based on the reproduction, a 42-day EC₅₀ of 22.0 mg Hg kg^-1 dry wt was observed for E. albidus while for F. candida the 28-day EC₅₀ was 3.26 (2.45-4.05) mg Hg kg^-1 dry wt. Although these data can be considered as a step forward in the assessment of the potential risks of mercury in terrestrial environments, further research is needed to evaluate the influence of soil parameters on the toxicity of mercury and to quantify the effect of ageing on the bioavailability.     

Acute toxicity of water soluble fractions derived from a coal liquid (SCR-II) to three aquatic organisms

Acute toxicity screening tests were conducted with water soluble fractions (WSFs) of a solvent refined coal (SRC-II) liquid from a pilot plant and three reference organisms: the cladoceran Daphnia magna, the fathead (FH) minnow Pimephales promelas, and larvae of the midge fly Chironomus tentans. Stock WSFs typically contained 900 to 1100 mg l^?1 total carbon (TC) and 700 to 800 mg l^?1 total dye complexable phenolics, with lower concentrations of aromatic and saturate hydrocarbons and N compounds. Under standard test conditions (temperature 20 °C, pH 7.3 to 8.2 and hardness 65 to 80 mg l^?1 CaCO₃), mean LC50 values in mg l^? TC were 3.3 for daphnia, 11.l for FH minnow, and 13.7 for midge larvae. Acute toxicity was also examined under other water quality conditions (temperature 10 or 25 °C, pH 6.0 or 6.5, and hardness ? 180 to 220 mg 1^?1 CaCO₃). The coal liquid was less toxic to daphnids at 10 °C than at 20 or 25 °C, but response of other organisms at different temperatures varied. The pH of the liquid had little effect on toxicity values. All organisms were less susceptible in hard water. Chemical compositions of stock WSFs were similar, suggesting that temperature, pH, and hardness had little effect on solubility of major synfucl components. Dilution indexes for stock WSFs were higher than for petroleum oils, and reflect the greater solubility of chemicals from the liquified coal in freshwater.     

Toxicity of Sb and Cu in Sewage Sludge to Terrestrial Plants (Lettuce,Oat, Radish), and of Sludge Elutriate to Aquatic Organisms (Daphnia and Lemna) and its Interaction

Antimony (Sb) and Copper (Cu) are two metals of major concern in sewage sludge. Antimony because its use in society is increasing and this might lead to increased Sb concentrations in sludge. Copper because its total volume in use in society is large and because of corrosion from water pipes it is most difficult to reduce the Cu concentrations in sludge. Fresh digested sewage sludge was spiked with Cu or Sb and the sludge was cultivated with oat (Avena sativa), lettuce (Lactuca sativa) or radish (Raphanus sativus). Elutriates from the cultivated sludge were tested for toxicity with Lemna minor (7-d growth) and Daphnia magna (48 h immobility). Before cultivation the elutriates were toxic to Lemna and Daphnia due to high concentrations of ammonia (NH₃) and nitrite (NO₂ ^-). Cultivation decreased the concentrations of both NH₃ and NO₂ ^-, thereby reducing the impact of these compounds in the toxicity tests. Cultivation also decreased the metal concentrations and pH. Daphnia magna was the most sensitive test organism in this study with a 48 h EC₅₀ of 1130 mg Cu kg^-1 dry wt and 5 mg Sb kg^-1 dry wt in elutriates from sludge cultivated with oat. In sludge cultivated with radish the 48 h EC₅₀ was 1700 mg Cu kg^-1 dry wt and 22 mg Sb kg^-1 dry wt. The effect of Cu could be predicted by pH and Cu concentrationin the elutriate, but the effect of Sb could not solely be explained by its concentration in the elutriate.     

Quality of Tigris River passing through Baghdad for irrigation

The effect of Baghdad city on the water quality of the Tigris River was studied from April 1977 to March 1978. The chemical and physical characteristics of the water which are necessary in judging the quality of water for irrigation were studied. It was found that Baghdad was responsible for increasing the water salinity from 390 to 443 mg l^?1. Total hardness and turbidity were increased when the river passed through Baghdad. The increase in the total hardness was mostly due to the increase in Mg concentration. The results also suggested that there should be no problem from the heavy metals or inorganic N in this water when used for irrigation. The Tigris River water in Baghdad was classified as classC ₂ S ₁; that is water of second class with regard to salinity and first class with regard to sodicity.     

Acute and sub-chronic toxicity of lead to the early life stages of smallmouth bass (Micropterus Dolomieui)

The early life stages of smallmouth bass (Micropterus dolomieui) were exposed to Pb in acute (96 hr) and sub-chronic (90 day) bioassays (water hardness = 152 mg L^?1 as CaCO₃). After 96-hr static exposures at nominal Pb concentrations up to 15.9 mg L^?1, eggs and sac fry showed no increased mortality over that in controls. Swim-up fry (96-hr LC₅₀ = 2.8 mg Pb L^?1) were more sensitive to Pb exposure than were fingerlings (96-hr LC₅₀ of 29.0 mg Pb L^?1 ). The relation between dissolved Pb and mortality was non-significant for either swim-up fry or fingerlings. Fingerlings were exposed to Pb concentrations as high as 405 μg L^?1 for 90 day to evaluate effects on substrate selection, locomotor activity, hematology, and weight. Dark or light substrate selection (cover-seeking) and locomotor activity, weight and hemoglobin concentration in the blood were not significantly altered by any treatment. Hematocrit and leucocrit varied significantly but not in relation to Pb levels. Sub-chronic Pb exposure did not appear to represent a threat to smallmouth bass in waters of medium hardness and above-neutral pH (7.1 to 7.9).     

Phytotoxicity of some chloroanilines and chlorophenols, in relation to bioavailability in soil

Soil adsorption and the effect of four chlorophenols and three chloroanilines on the growth of lettuce (Lactuca sativa) were determined in two soil types differing in organic matter content and pH. Adsorption increased with increasing organic matter content of the soils. Phytotoxicity, based on dosed amounts, was significantly higher in the soil with the low level of organic matter. This difference could be reduced by recalculating the EC₅₀ values for the effect of the test substances on plant growth in mg kg-1 dry soil towards concentrations in mg L-1 pore water using data from soil adsorption experiments. For pentachlorophenol only this recalculation increased rather than decreased the difference between the two soils, however, when the EC50 values for pentachlorophenol were corrected for the difference in soil pH, almost the same values resulted for both soils. Calculated EC₅₀ values on the basis of pore water concentrations appeared to be in good agreement with values determined in nutrient solution tests. These results indicate that, for plants, the toxicity and therefore the bioavailability of organic chemicals in soil mainly depend on the concentration in the soil solution, and can be predicted on the basis of sorption data. Attempts to develop QSARs relating log EC₅₀ values in μmol L^?1 pore water with lipophilicity (expressed as the octanol/water partition coefficient: log K_ow,) of the test substances resulted in a statistically significant relationship. This relationship was further improved by correcting the chlorophenol data for dissociation effects.     

Impact of heavy metal amended sewage sludge on forest soils as assessed by bacterial and fungal biosensors

Bacterial and fungal bioluminescence-based biosensors were used as indicators of potential heavy metal toxicity to microorganisms in the needle litter of a mature Pinus radiata forest under heavy metal contaminated sewage sludge. Sewage sludge was amended with increasing concentrations of Cu, Ni and Zn and applied to the surface of a mature P. radiata forest. The response of the bacterial and fungal biosensors to soluble Cu, Ni and Zn in needle litter extracts was investigated. The bioluminescence response of the bacterial biosensor Escherichia coli HB101 pUCD607 declined as water-soluble Zn concentrations increased. The effective concentrations that gave a 50% reduction in bioluminescence (EC₅₀ values) for water-soluble Zn and total litter Zn were 1.3 mg l⁻¹ and 3700 mg kg⁻¹, respectively. The bioluminescence response of the fungal biosensor Armillaria mellea declined as soluble Cu concentrations increased. The EC₅₀ values for water-soluble Cu and total litter Cu were 0.12 mg l⁻¹ and 540 mg kg⁻¹, respectively. No decline in bioluminescence was noted for either the bacterial or fungal biosensor on exposure to increasing concentrations of water-soluble Ni. The use of a combination of bacterial and fungal biosensors offers a rapid and sensitive tool for assessing toxicity of heavy metals to microorganisms and, thus, elucidating the environmental impact of contaminants in sewage sludge on litter dwelling microorganisms.     

Effects of a chromated-copper-arsenate wood preservative on the growth of a pentachlorophenol degrading bacterium

A chromated-copper-arsenate (CCA) wood preservative was tested for toxic effects on the growth of a bacterial culture (Flavobactenum sp. ATCC 53874) capable of biodegrading pentachlorophenol, another wood preservation chemical. Both a commercially available CCA preparation and a laboratory-prepared CCA solution were tested. Each had an inhibitory effect on the growth of Flavobacterium at diluted CCA levels as low as 1.0×10^?4 to 1.0×10^?5% wt vol^?1. The commercial formulation was generally more toxic. EC₅₀ values calculated after 96 hr of incubation were 1.2 ×10^?4% wt vol^?1 for the commercial material (containing 0.15/0.097/0.14 μg mL^?1 of Cr/Cu/As, respectively) and 3.8×10^?4% for the laboratory solution (containing 0.51/0.31/0.49 μg mL^?1 of Cr/Cu/As, respectively). CCA toxicity increased during the first 7 to 8 days and then slowly decreased for the balance of the 21 day incubation period. Biodegradation of pentachlorophenol residues in contaminated soil will be negatively affected by the presence of CCA as a co-contaminant.     

Bio-accumulation and metabolic effects of zinc on marine fouling dreissinid bivalve,Mytilopsis sallei (Recluz)

Zinc (Zn) toxicity to a marine fouling dreissinid bivalveMytilopsis sallei was investigated and the safe concentration of Zn was determined for this bivalve. In acute toxicity tests onM. sallei the 96 h LC₅₀ value for Zn is found to be 8.364 mg 1^?1. The results suggest that Zn has the lowest toxic effect onM. sallei when compared to copper and mercury. Effect of Zn on the oxygen consumption ofM. sallei was studied. Sub-lethal concentrations of Zn functioned as respiratory depressants. Accumulation of Zn was investigated in relation to exposure period and concentration inM. sallei. Zn accumulation was found to be sensitive to both concentration of Zn and exposure time. The effect of exposure time and concentration on body biochemical components was also studied inM. sallei. This accumulated Zn has resulted in impairment of carbohydrate metabolism and protein utilisation.     

Responses of Photosynthetic Efficiency,Cell Shape and Motility in Euglena gracilis (Euglenophyceae) to Short-Term Exposure to Heavy Metals and Pentachlorophenol

Euglena gracilis was exposed for 24 hr to concentrationsof copper, nickel, lead and zinc ranging from 0.1 to 2.0 mg L^-1 and to pentachlorophenol ranging from 0.1 to 10.0 mg L^-1. Photosynthetic efficiency (PE) was inhibited by increasing concentrations of the heavy metals. Nickel was foundto be the least toxic of the metals to E. gracilis, whilethe other three metals exhibited similar levels of toxicity. Treatment with pentachlorophenol caused unusual responses of the photosynthetic apparatus probably due to the especially high toxicity of this substance. Both cell shape and motility turned out to be insensitive physiological parameters for the toxicity testing of the substances studied.