David L. DeFoe

Effect of Polychlorinated Biphenyl Compounds on Survival and Reproduction of the Fathead Minnow and Flagfish

Abstract Two 9-month continuous-flow bioassays and several intermediate length continuous-flow tests were conducted to determine safe levels of Aroclor 1242, 1248, and 1254 for the fathead minnow (Pimephales promelas) and Aroclor 1248 for the flagfish, Jordanella floridae. Calculated 96-hr LC50 values for newly hatched fathead minnows were 7.7 μg/liter for Aroclor 1254 and 15 μg/liter for 1242. Three-month-old fatheads had a 96-hr LC50 of 300 μg/liter for 1242. Reproduction occurred at and below 1.8 μg/liter 1254 and at and below 5.4 μg/liter 1242. Newly hatched young were the most sensitive life stage. Growth of young fatheads was also affected above 2.2 μg/liter 1248, and none survived above 5.1 μg/liter after 30 days. Young flagfish did not survive at 1248 concentrations above 5.1 μg/liter and did not grow well above 2.2 μg/liter. Tissue residues in fathead minnows ranged from 0.7 μ/g 1248 in control fish to 1036 μ/g 1254 in fish held for 8 months in water containing 4.6 μg/liter 1254.

Comparative toxicity of arsenic compounds and their accumulation in invertebrates and fish

The toxicity of arsenic III, arsenic V, sodium dimethyl arsenate, and disodium methyl arsenate to stoneflies, snails, amphipods, and trout, and the bioaccumulation of these compounds were studied during a 28-day flow-through test.Daphnia magna were exposed for 21 days in static tests to determine life-cycle effects. All animals were exposed to concentrations of approximately 100 and 1000μg/L (as arsenic) of each of the compounds. Arsenic III, the most toxic compound, caused a significant reduction in the survival of amphipods at 1000μg As/L after seven days. None of the compounds significantly affected the survival of other test species after 28 days or reduced young production inDaphnia after 14 days of exposure. The concentration of accumulated arsenic in stoneflies, snails,and Daphnia was as much as 131, 99, and 219 times greater than the water concentration, whereas amphipods and rainbow trout contained arsenic residues similar to the controls. Residues in stoneflies, snails, andDaphnia exposed to 1000μg As/L were higher than those in animals exposed to 100μg As/L, but appeared to reach a steady state after 14 days. Total arsenic accumulation was greatest in organisms exposed to inorganic arsenic, particularly at 100μg/L.

Chronic Effects of Cadmium and Zinc Mixtures on Flagfish (Jordanella floridae)

Abstract Flagfish were exposed to cadmium and zinc as individual metals and as mixtures (4.3-8.5 μg Cd/liter and 73.4-139 μg Zn/liter) through one complete life cycle in Lake Superior water (45 mg/liter total hardness). Cadmium and zinc did not act additively at sublethal concentrations when combined as mixtures; however, a joint action of the toxicants was indicated. Effects on survival showed that the toxicity of cadmium and zinc mixtures was little if any greater than the toxicity of zinc alone. Mechanisms of zinc toxicity in this test were similar to those in previous chronic tests of individual metals, indicating that the presence of cadmium did not influence the mode of action of zinc. Comparisons between metal residues in fish exposed to each individual metal or to the metal mixtures showed that the uptake of one metal was not influenced by the presence of the other.

Ambient Solar UV Radiation Causes Mortality in Larvae of Three Species of Rana Under Controlled Exposure Conditions

Abstract Recent reports concerning the lethal effects of solar ultraviolet-B (UV-B) (290–320 nm) radiation on amphibians suggest that this stressor has the potential to impact some amphibian populations. In this study embryos and larvae of three anuran species, Rana pipiens, Rana clamitans and Rana septentrionalis, were exposed to full-spectrum solar radiation and solar radiation filtered to attenuate UV-B radiation or UV-B and ultraviolet-A (UV-A) (290–380 nm) radiation to determine the effects of each wavelength range on embryo and larval survival. Ambient levels of solar radiation were found to be lethal to all three species under exposure conditions that eliminated shade and refuge. Lethality was ameliorated by filtration of UV-B radiation alone, demonstrating that ambient UV-B radiation is sufficient to cause mortality. Although several studies have qualitatively demonstrated the lethality of UV-B to early life stage amphibians this study demonstrates that the larval life stages of the three species tested are more sensitive than the embryonic stages. This suggests that previous reports that have not included the larval life stage may underestimate the risk posed to some anuran populations by increasing UV-B exposure. Furthermore, this study reports quantitative UV-B dosimetry data, collected in conjunction with the exposures, which can be used to begin the assessment of the impact of environmental changes which increase UV-B exposure of these anurans.

Saturation units for use in aquatic bioassays.

Methods were developed for preparing liquid/liquid and glass wool column saturators for generating chemical stock solutions for conducting aquatic bioassays. Exposures have been conducted using several species of fish, invertebrate, and mollusks in static and flow-through conditions using these methods. Stock solutions for 82 organic chemicals were prepared using these saturation units. The primary purpose of stock generation was to provide a continuous and consistent amount of toxicant laden solution at a measured analytical level which would be available to test organisms for the test duration. In the present study, the glass wool column and liquid/liquid saturators were used to provide consistent stock concentrations, at times approaching saturation, for fathead minnow (Pimephales promelas) acute exposures. Attempts were made to achieve the maximum solubility of these compounds for comparison purposes to water solubility values available in the literature. Literature solubility values from a database by Yalkowsky et al. [1] provided information on temperatures and data quality which allowed comparison to values obtained from the present study. Twenty four compounds were identified and analyzed for the comparison of maximum obtainable solubility levels. Maximum saturator stock water concentrations were generally lower (R = 0.98) but were in close agreement with published water solubility values.

Toxicity and bioaccumulation of endrin and methoxychlor in aquatic invertebrates and fish

Abstract Stoneflies, caddis-flies, isopods, snails and bullheads were exposed to endrin or methoxychlor in a flowing-water test system for 28 days. Endrin was more toxic than methoxychlor. Behaviour changes in the caddis-fly Brachycentrus americanus and in the stonefly Pteronarcys dorsata were observed within 4 days at 0·07 and 0·15 μg/litre of endrin, respectively. The LC50 values decrease with increasing exposure times. The 28-day LC50 was less than 0·03 μg/litre for B. americanus and 0·07 μg/litre for P. dorsata. The 28-day LC50 for the bullhead Ictalurus melas was 0·10 μg/litre. Methoxychlor, at the concentrations tested, did not affect all the species. The isopod Asellus communis was the most sensitive; behavioural changes occurred within the first 4 days. The 28-day LC50 was 0·42 μg/litre. The LC50 for the caddis-fly Hydropsyche sp. decreased from 2·9 μg/litre at 14 days to 1·3 μg/litre at 28 days. The stonefly P. dorsata and the snail Physa integra did not die at the highest concentration tested (4·2 μg/litre), although behavioural changes were seen at 2·2 μg/litre for the stonefly. Pesticide accumulation was determined in the stoneflies and snails that survived the exposures. Stoneflies accumulated methoxychlor and endrin to concentrations 350 to 1150 times greater than the water concentrations. The snail concentration factors for methoxychlor ranged from 5000 to 8600.

Influence of storage time on toxicity of freshwater sediments to benthic macroinvertebrates

Guidance concerning recommended storage times for sediments to be used in toxicity tests generally has not been based upon systematically collected experimental data. The objective of this study was to better define the effects of storage time on toxicity of a series of freshwater sediments. Sixteen sediments with varying types of contaminants were collected, homogenized and stored at 4 degrees C in 1 liter aliquots, which were periodically tested for toxicity to the amphipod Hyalella azteca and the midge Chironomus tentans after storage times of up to 101 weeks. The sediments ranged from non-toxic to extremely toxic (100% mortality) in 10-day assays, with several of the samples displaying an intermediate degree of toxicity (e.g. partial mortality, reduced growth). Biological responses in most of the samples did not vary with time relative to their statistical relationship to control values; samples identified initially as toxic (or non-toxic) tended to remain toxic (or non-toxic) regardless of when they were tested. The variations that were observed in biological responses over time generally were not systematic; that is, there were no apparent trends in samples becoming more (or less) toxic in the 10-day assays. This suggests that the source of at least some of the temporal changes in toxicity were due to inherent biological variability of the assays used to assess the sediments, rather than the effects of storage. In C. tentans tests with the least toxic sediments, among-replicate variability tended to be greater in initial assays than in tests with samples that had been stored for some period of time. This may have been due to the presence of indigenous competitive or predatory organisms that did not survive during prolonged storage.