Robert W. Winner

Bioaccumulation and toxicity of copper as affected by interactions between humic acid and water hardness

Abstract This study evaluated the effects of water hardness and humic acid (HA) on the acute and chronic toxicity of copper to Daphnia pulex and on its accumulation by D. magna . Hardness had little effect on either the acute (3-day) or the chronic (42-day) toxicity of copper. Humic acid significantly reduced both the acute and chronic toxicity of copper when added to waters having hardnesses of 58, 115 and 230 mg l −1 as CaCO 3 . The effect, per unit of HA, on chronic toxicity was very similar for soft and medium water but less in hard water. At each of two HA concentrations, copper was chronically more toxic in hard water than in either medium or soft water. Bioaccumulation of copper varied with relative hardness and HA concentration and this was further affected by age at exposure. For 1-day-old animals, an increase in either hardness or HA- or any combination of the two, tended to decrease bioaccumulation. Results for 7-day-old animals were in general agreement except for animals exposed to copper in hard water at an intermediate HA concentration. These animals accumulated significantly more copper in the presence of HA. This agrees with the fact that this concentration of HA also increased the chronic toxicity of copper in hard water. Both of those phenomena are probably due to the displacement of Cu 2+ from HA by competition from the increased concentrations of Ca 2+ and Mg 2+ . The fact that HA had the opposite effect on copper accumulation by young animals in hard water could not be explained.

The toxicity and bioaccumulation of cadmium and copper as affected by humic acid

Abstract The toxicity of Cd and Cu to daphnids was evaluated over a 42-day exposure period at three humic acid concentrations. The addition of humic acid to test water decreased the acute and chronic toxicity of Cu but increased the acute and chronic toxicity of Cd. However, there was no effect of HA on the bioaccumulation of either metal. At the highest concentration, the presence of humic acid actually resulted in an increase in mean brood sizes of Cu-exposed animals and prevented a reduction in mean brood sizes of Cd-exposed animals.

Acute toxicity of copper to three life stages of Chironomus tentans as affected by water hardness-alkalinity

Abstract The acute toxicity of copper to first-and fourth-instar larvae of the midge Chironomus tentans was determined in soft, medium and hard water (43, 110 and 172 mg litre −1 as CaCO 3 total hardness, respectively). Percentage hatch of C. tentans eggs as influenced by copper concentration was studied in soft and hard water. Fourth instars were 12–27 times more resistant to copper stress than were first instars. Eggs were much more resistant to copper than either larval stage. Water hardness-alkalinity had a significant effect on copper toxicity to both larval instars. The concentration of copper necessary to immobilise 50% of the test population after 96 h (96-h EC 50 ) was not significantly different in soft and medium water (16·7 and 36·5 μg Cu litre −1 , respectively) for first-instar larvae, but both were significantly less than in hard water (98·2 μg Cu litre −1 ). Mean 96-h EC 50 s for fourth-instar larvae were not significantly different in medium (997·5 μg Cu litre −1 ) and hard (1184·6 μg Cu litre −1 ) water, but both were significantly higher than in soft (211·8 μg Cu litre −1 ) water. The influence of hardness-alkalinity on hatching success was less apparent. Percentage hatch in soft water was significantly reduced only at 5000 μg C litre −1 , while in hard water, percentage hatch was not affected even at that copper concentration. If sensitivity to copper is representative of sensitivity to other chemicals, the practice of using fourth-instar larvae in toxicity tests may grossly underestimate the sensitivity of the species to toxicants.

Relationship between chronic toxicity and bioaccumulation of copper, cadmium and zinc as affected by water hardness and humic acid

Abstract Using daphnids, we have evaluated the effects of water hardness and humic acid (HA) on the chronic toxicity and bioaccumulation of Cu, Cd and Zn. Although changes in water hardness and HA concentration changed bioaccumulation or chronic toxicity, or both, of each of the three metals, there was no consistent relationship between changes in toxicity and changes in bioaccumulation. Only for Cu in hard water was there a positive correlation between toxicity and bioaccumulation. The uptake of 65Zn by molted exoskeletons suggests that changes in water chemistry do indeed modify the bioavailability of metals as would be expected. That is, an increase in the concentration of Ca2+ or Mg2+ or the increased chelation of metals by HA should decrease bioavailability. The complex storage, transformation and excretion processes in multicellular animals, however, result in there being a poor correlation among bioavailability, bioaccumulation and toxicity.

Filtration and phototactic behavior as indices of chronic copper stress inDaphnia magna straus

Filtration rate and negative phototactic behavior ofDaphnia magna were evaluated as potential predictors of the chronic no-effect copper concentration. The effects of copper on filtration and phototactic behavior were compared to the effects of chronic copper exposure on survivorship, number of juvenile molts, age at reproductive maturity, and neonate body length. Animals exposed to copper concentrations ⩾20μg/L exhibited reductions in filtration rate, negative phototaxis, body length of neonates and survival time. Animals exposed to 10μg/L exhibited a reduction in filtration rate, negative phototaxis and body length of neonates, but not in survival time. Number of juvenile molts, age at reproductive maturity, and mean brood size each responded erratically to copper exposure and are poor indices of copper stress. Since phototactic behavior, filtration rate, and neonate body length were all reduced at copper concentrations which did not reduce longevity or reproduction, bioassays in which only the latter are examined may underestimate the toxicity of copper and other chemicals. This may occur if bioassays are conducted for the frequently chosen 21-day interval.

Effects of water hardness and humic acid on zinc toxicity to Daphnia magna Straus

Abstract The effects of water hardness and humic acid (HA) on the acute and chronic toxicity of zinc to Daphnia magna were evaluated. Increases in either water hardness or HA concentration resulted in proportional decreases in both acute (3-day) and chronic (50-day) zinc toxicity. The effect of either of these variables (hardness or HA) was independent of the other in acute tests. In chronic tests, HA reduced the toxic effect of zinc on reproduction more in soft water than in hard water. In addition to reducing the chronic toxicity of zinc, our data suggest that an increase in water hardness also changes the mode of chronic toxic action of zinc. As previously shown for other metals, this study indicates that a reliance on only reproductive and survival endpoints in short-duration chronic tests may lead to an underestimation of the chronic toxicity of zinc.

Toxicity of copper to the green alga, Chlamydomonas reinhardtii (Chlorophyceae), as affected by humic substances of terrestrial and freshwater origin

Abstract Population growth, loss of flagella and encystment were used as indices of copper toxicity to Chlamydomonas reinhardtii . Copper concentrations up to 64 μg/l had no effect on population growth in any of the treatments. Deflagellation occurred at copper concentrations ranging from 6.7 to 25.4 μg/l with terrestrial humic acid (HA) having the greatest effect on toxicity and aqueous fulvic acid (FA) having no effect on toxicity. The effect of aqueous HA was intermediate. Encystment was a less sensitive index of copper toxicity than was defiagellation but it may offer protection against extinction when algae are exposed to pulses of higher copper concentrations. Based on our results, we conclude that terrestrially derived humic acids are an inappropriate model to be used in predicting the effects of freshwater humic substances oa the toxicity of metals.

A comparison of body length, brood size and longevity as indices of chronic copper and zinc stresses in Daphnia magna

Abstract An evaluation of data from copper and zinc bioassays with Daphnia magna indicates that concentrations which have an adverse effect, as measured over a lifetime exposure, also cause a significant reduction in growth measured as body length of primiparous females. Both body length and longevity were more sensitive indices of chronic stress than was reproduction.

Interactive effects of water hardness and humic acid on the chronic toxicity of cadmium to Daphnia pulex

Abstract The chronic toxicity of Cd was reduced by an increase in water hardness from 58 to 116 mg/l; a further increase in hardness to 230 mg/l, however, had no further effect on chronic Cd toxicity. The most consistent and sensitive index of chronic Cd stress was the abortion of young. Based on this index, 0.75 or 1.50 mg/l humic acid had no effect on the chronic toxicity of Cd in either the soft or medium-hard test-waters. This was also true for 0.75 mg/l humic acid in hard water; however, the addition of 1.5 mg/l humic acid to hard water resulted in an increase in the chronic toxicity of Cd. In conjunction with Cd exposures greater than the chronic no-effect concentration, the addition of either 0.75 or 1.50 mg humic acid per liter to water of any of the three hardnesses usually increased the mortality rate over a 42-day exposure period. The mechanism by which humic acid increases the abortion rate in hard water and increases mortality rate in soft, medium-hard and hard water is unknown.

Relative sensitivity of Cerodaphnia dubia laboratory tests and pond communities of zooplankton and benthos to chronic copper stress

Abstract In situ enclosure experiments were conducted in a pond in southwestern Ohio during spring, 1987, to evaluate the effects of copper on zooplankton and benthos. Total copper concentrations (0, 20 and 40 μg 1−1) were maintained in enclosures for a 5-wk period. In the laboratory, 7-day Ceriodaphnia tests were also conducted to evaluate this tests ability to predict copper-induced changes in field enclosure communities. Colonies of the alga, Uroglena, were significantly lower in 20 and 40 μg 1−1 copper treatments than in controls. The benthos community included snails, fingernail clams, mayflies, and midges, but densities of only small mayflies and chironomids were affected by copper (40 μg 1−1). The zooplankton community was strongly affected by both copper concentrations. Rotifiers and cyclopoid and calanoid copepods exhibited significant reductions in density in both copper treatments. Daphnia, however, achieved highest densities in the 20 μg 1−1 copper treatment and completely disappeared from controls. This unexpected response was accurately predicted by the 7-day Ceriodaphnia test, but this same test did not predict that other taxa would be more sensitive than Daphnia. We conclude that community responses are complex and cannot be reliably predicted with single-species toxicity tests.