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A model mesocosm system was used to simulate the effect of endosulfan entering a waterway from episodic events such as accidental overspray or in runoff water containing contaminated sediment following storm events. The fate of technical endosulfan applied to a 24-stream mesocosm was compared in experiments where the pesticide was applied either directly as water contamination or after being pre-bound to sediment. The flow of water through the streams was discontinued for a 10-12 h period following the pesticide application. Following the water application, only approximately 3% of endosulfan remained in the streams after 4 days and then was not detectable after 7 days. In contrast, after application pre-bound to sediment, approximately 33% of the endosulfan remained in the streams after 4 days and 14% after 7 days. Additionally, with the sediment-bound application, the proportion of endosulfan was higher in the substrate (11%) after 7 days than in the overlying water (3%), and approximately 1% was oxidised to the sulphate form. The dissipation of endosulfan in the water column of both experiments followed a two-parameter exponential decay model characterised by a relatively fast first-order single-phase process. In sediment of both experiments and the gravel of the sediment-dosing experiment, the dissipation of endosulfan followed more closely a four-parameter bi-exponential decay model characterised by first-order kinetics of two fractions: the first fraction dissipates quickly, and in the longer term the second fraction dominates the overall dissipation with a slower rate. In the gravel section of the water-dosing experiment, endosulfan dissipation was characterised by relatively very slow two-parameter exponential decay. The overall dissipation rates of the alpha- and beta-endosulfan isomers were significantly higher in the water-dosing than in the sediment-dosing experiment, except in the gravel section of the mesocosm. The uptake of the endosulfan into passive samplers constructed from polyethylene membrane bags containing trimethylpentane solvent (TRIMPS) placed in the overlying water was linear. In contrast, TRIMPS buried in sediment failed to uptake endosulfan from the sediment substrate, indicating that short-term deployment of passive samplers can only be used to determine time-weighted average concentrations of bioavailable chemicals in the water column. A 34-h LC50 of 2.8 microg/l [95% confidence interval (CI) 1.5-4.2 microg/l] for juveniles of the native fish Macquaria ambigua was obtained when exposed during the water-dosing experiment. This study demonstrated that the pulse entry of sediment contaminated with endosulfan into a receiving waterway was more persistent compared with direct aqueous contamination and the endosulfan would be bioavailable to pelagic organisms following a gradual partitioning to the water column.

Cigarette butts are the most numerically frequent form of litter in the world. In Australia alone, 24-32 billion cigarette butts are littered annually. Despite this littering, few studies have been undertaken to explore the toxicity of cigarette butts in aquatic ecosystems. The acute toxicity of 19 filtered cigarette types to Ceriodaphnia cf. dubia (48-hr EC50 (immobilization)) and Vibrio fischeri (30-min EC50 (bioluminescence)) was determined using leachates from artificially smoked cigarette butts. There was a 2.9- and 8-fold difference in toxicity between the least and most toxic cigarette butts to C. cf. dubia and V. fischeri, respectively. Overall, C. cf. dubia was more inherently sensitive than V. fischeri by a factor of approximately 15.4, and the interspecies relationship between C. cf. dubia and V. fischeri was poor (R(2) = 0.07). This poor relationship indicates that toxicity data for cigarette butts for one species could not predict or model the toxicity of cigarette butts to the other species. However, the order of the toxicity of leachates can be predicted. It was determined that organic compounds caused the majority of toxicity in the cigarette butt leachates. Of the 14 organic compounds identified, nicotine and ethylphenol were suspected to be the main causative toxicants. There was a strong relationship between toxicity and tar content and between toxicity and nicotine content for two of the three brands of cigarettes (R(2 )0.70) for C. cf. dubia and one brand for V. fischeri. However, when the cigarettes were pooled, the relationship was weak (R(2)0.40) for both test species. Brand affected the toxicity to both species but more so for V. fischeri.

The toxicity of the organochlorine pesticide endosulfan to macroinvertebrate communities was tested using a system of 24 artificial streams. Macroinvertebrate communities in the streams were exposed to a range of endosulfan concentrations for a 12-h period and then monitored for 96 h. Endosulfan was prebound to fine river sediment and applied to the streams as a contaminated sediment slurry. This did not cause changes in the structure of benthic communities; however, significant changes (P

Bicarbonate is often a major ionic constituent associated with produced waters from methane gas extraction and coal mining, yet few studies have determined its specific toxicity. Currently, the environmental risk of bicarbonate anion in water discharges is assessed based on the toxicity of sodium chloride or artificial seawater and is regulated via electrical conductivity. Increased NaHCO(3) added to Ceriodaphnia dubia in synthetic or natural water gave similar 48-h 10% effective concentration (EC10) values of 1750 ± 125 mg NaHCO(3)/L (mean ± standard error) and 1670 ± 180 mg NaHCO(3)/L, respectively. Bicarbonate was toxic to C. dubia in both waters with conductivities above 1900 µS/cm. In contrast, when conductivity was elevated with NaCl, toxicity to C. dubia was observed only above 2800 µS/cm. Bicarbonate also impaired C. dubia reproduction with an EC10 of 340 mg NaHCO(3)/L. Major ion composition also influenced Zn bioavailability, a common co-occurring metal contaminant in coal mine waters, with sublethal concentrations of NaHCO(3) and elevated pH increasing Zn toxicity. Higher pH was the dominant parameter determining a 10-fold increase in the 48-h 50% effective concentration (EC50) for Zn toxicity to C. dubia at pH 8.6 of 34 µg Zn/L (95% confidence limit = 32-37 µg Zn/L) compared with the Zn toxicity at approximately circumneutral pH. Exposure of the freshwater shrimp Paratya australiensis (Atyidae) in natural water to increasing bicarbonate gave a mean 10-d 10% lethal concentration (LC10) of 850 ± 115 mg NaHCO(3)/L, associated with a mean conductivity EC10 of 1145 µS/cm, which is considerably lower than toxicity of NaCl and artificial seawater to this species reported elsewhere. Because toxicity was influenced by salt composition, specific ions should be regulated rather than conductivity alone in mine wastewater discharges.

The widespread use of chlorpyrifos for pest control in urban and rural environments poses a risk of contamination to aquatic environments via runoff, spray drift or spillage. The aim of this study was to assess the fate of chlorpyrifos and its toxicity to common freshwater invertebrates in the laboratory and in stream mesocosms. Chlorpyrifos was rapidly lost from the test systems but the rates of loss varied considerably, such that losses in the mesocosms could not be reliably predicted from the static laboratory studies. This was likely due to the mass transport of chlorpyrifos from the mesocosm via stream flow. Chlorpyrifos was acutely toxic to all invertebrates tested with the cladoceran species (laboratory 48 h LC50 values 0.07–0.10 μg L−1) being most sensitive. Despite the differences in the dynamics of chlorpyrifos in the laboratory and mesocosm systems, the sensitivities of the mayfly Atalophlebia australis and the cladoceran Simocephalus vetulus were similar in the 2 systems.

The toxicity of the organochlorine pesticide endosulfan to macroinvertebrate assemblages was tested using a system of 24 artificial streams. In separate experiments, the effects of 12- and 48-h exposure to aqueous endosulfan were assessed. No-observed-effect concentrations (NOEC) for endosulfan on macroinvertebrate assemblages were 8.69 and 1.00μg/L for the 12- and 48-h exposure studies, respectively. In both studies, changes were driven by reduced abundances of the mayfly, Jappa kutera. Algal blooms occurred in the 48-h exposure experiment in streams that received the 6.87 or 30.70μg/L treatments. These effects occurred at concentrations that might occur as a result of episodic events such as accidental overspray or rainstorms. By establishing a causal link between endosulfan and changes to macroinvertebrate assemblages, this study adds further weight to the hypothesis that endosulfan is a major contributor to changes observed in rivers of the cotton-growing region of New South Wales, Australia during the pesticide spray season. © 2003 Elsevier Science (USA). All rights reserved.

Recent investigations into the level of heavy metal enrichment in the sediments of Lake Macquarie have indicated that significant contamination has occurred over the past 100 years, with elevated levels of lead, zinc, cadmium, copper, and selenium being observed in most parts of the lake. Pore water extracted from sediments showing the greatest contamination by these metals exhibited toxicity to the larval development of the sea urchin Heliocidaris tuberculata. However, an analysis of pore water metal concentrations revealed that the concentrations of these metals were too low to cause toxicity. Rather, pore water toxicity was highly correlated with manganese for the majority of sites sampled; subsequent spiking experiments confirmed manganese as a cause of toxicity. Current levels of manganese in the sediments of Lake Macquarie have arisen from natural sources and are not the result of anthropogenic activities. These results reiterate the importance of identifying the causes of toxicity in assessments of sediment contamination, particularly when testing sediment pore waters using sensitive early life stages.

This study determined the influence of key water chemistry parameters (pH, alkalinity, dissolved organic carbon [DOC], and hardness) on the aqueous speciation of copper and zinc and its relationship to the acute toxicity of these metals to the cladoceran Ceriodaphnia cf dubia. Immobilization tests were performed for 48-h in synthetic or natural waters buffered at various pH values from 5.5 to 8.4 (other chemical parameters held constant). The toxicity of copper to C. cf dubia decreased fivefold with increasing pH, whereas the toxicity of zinc increased fivefold with increasing pH. The effect of DOC on copper and zinc toxicity to C. cf dubia was determined using natural fulvic acid in the synthetic water. Increasing DOC was found to decrease linearly the toxicity of copper, with the mean effect concentration of copper that immobilized 50% of the cladocerans (EC50) value 45 times higher at 10 mg/L, relative to 0.1 mg/L DOC at pH 6.5. In contrast, the addition of 10 mg/L DOC only resulted in a very small (1.3-fold) reduction in the toxicity of zinc to C. cf dubia. Copper toxicity to C. cf dubia generally did not vary as a function of hardness, whereas zinc toxicity was reduced by a factor of only two, with an increase in water hardness from 44 to 374 mg CaCO3/L. Increasing bicarbonate alkalinity of synthetic waters (30-125 mg/L as CaCO3) decreased the toxicity of copper up to fivefold, which mainly could be attributed to the formation of copper-carbonate complexes, in addition to a pH effect. The toxicity of copper added to a range of natural waters with varying DOC content, pH, and hardness was consistent with the toxicity predicted using the data obtained from the synthetic waters.