Laboratory evaluation of the toxicity of Perfluorooctane Sulfonate (PFOS) on Selenastrum capricornutum,Chlorella vulgaris,Lemna gibba,Daphnia magna,and Daphnia pulicaria

Perfluorooctane sulfonate (PFOS) is an anthropogenic compound found in trace amounts in many environmental compartments far from areas of production. This, along with the highly persistent nature of PFOS, presents a concern for possible effects in aquatic ecosystems. The objective of this study was to determine the toxicity of PFOS in representative freshwater organisms. Toxicity testing using standard laboratory protocols was performed on the green algae Selenastrum capricornutum and Chlorella vulgaris, the floating macrophyte Lemna gibba, and the invertebrates Daphnia magna and Daphnia pulicaria. No observable effect concentration (NOEC) values were generated from the most sensitive endpoints for all organisms. Autotroph inhibition of growth NOEC values were 5.3, 8.2, and 6.6 mg/L for S. capricornutum, C. vulgaris, and L. gibba, respectively. The 48-h immobility NOEC values for D. magna and D. pulicaria were 0.8 and 13.6 mg/L, respectively. In comparison to immobility, the 21-day lethality NOEC for D. magna was 5.3 mg/L. Based on effect (immobility) values, the most sensitive of all test organisms was D. magna. The most sensitive organism based on 50% inhibition of growth (IC(50)) was L. gibba, with an IC(50) value of 31.1 mg/L determined from wet weight. This is 4.3 times less than the LC(50) for D. pulicaria, which was 134 mg/L. Significant adverse effects (p < or = 0.05) were observed for all organisms in concentrations >134 mg/L. The results indicate that under laboratory conditions PFOS is acutely toxic to freshwater organisms at concentrations at or near 100 mg/L. Based on known environmental concentrations of PFOS, which occur in the low ng/L to low microg/L range, there is no apparent risk to freshwater systems. However, further work is required to investigate long-term effects in these and other freshwater organisms.     

Screening of Organophosphate Insecticide Pollution in Water by Using Daphnia magna

A simple and rapid screening method using Daphnia magna Straus (water fleas) on the basis of their immobilization was developed for detecting pesticide pollution. The laboratory testing of the toxicity of 11 organophosphate insecticides to D. magna determined 50% inhibition concentration of mobility at 48 h of exposure (48-h EC₅₀) of 0.19 to 2.6 μg/L. The mobility of D. magna was inhibited in several river and stream waters sampled from May 1995 to February 1998 in Tokyo. Chemical analysis of the waters revealed that they were polluted by sub-ppb or ppb level of organophosphate insecticides. A significant relationship was observed between the immobilization of D. magna and the pollution level of the river and stream waters. The D. magna test could be used as a low-cost preliminary screening method for insecticide pollution.     

Response of the zooplankton community and environmental fate of perfluorooctane sulfonic acid in aquatic microcosms

Little is known regarding perfluorooctane sulfonic acid (PFOS) toxicity to freshwater organisms. This field evaluation aims to assess the toxicological risk associated with exposure to PFOS across levels of biological organization. The analysis of variance study was conducted in replicate (n = 3) 12,000 L outdoor microcosms. Multivariate techniques were used to assess the response of zooplankton community structure and dynamics, as well as a floating macrophyte, Lemna gibba. The zooplankton community was significantly affected (p < 0.05) by the treatment regime given by the Monte Carlo permutations for all sampling times. A community-level no-observable-effect concentration ([NOEC]community) of 3.0 mg/L was determined for the 35-day study, however, longer term studies are recommended. The most sensitive taxonomic groups, Cladocera and Copepoda, were virtually eliminated in 30 mg/L treatments after 7 d. The 42-d 50% inhibition concentration (IC50) for L. gibba frond number was 19.1 mg/L and the NOEC was 0.2 mg/L. Furthermore, we investigated the persistence of PFOS over 285 d in microcosms under natural conditions. Perfluorooctane sulfonic acid concentration showed no drastic reduction in any treatment microcosm over the entire study period, confirming that this compound undergoes little degradation in aquatic systems. Presently, there appears to be little hazard to these freshwater organisms at reported environmental concentrations.     

The sensitivity of two cladocerans to water quality variables: Salinity <467 mg NaCl/L and hardness <200 mg CaCO3/L

The sensitivity of two cladocerans,Daphnia magna andCeriodaphnia dubia to salinity <467 nig NaCl/L and hardness <200 mg CaCO₃/L is reported, using the three-brood test. The time it took the control animals to produce three broods was 9 days forC. dubia and 10 days forD. magna. No detrimental effect due to NaCl <467 mg/L was noted for either cladoceran. The LC₅₀ for hardness was, for both animals, >200 mg CaCO₃/L. However, at concentrations <9 mg CaCO₃/LC. dubia showed stress by losing one or two animals at each concentration below this amount. At hardness levels in excess of 70 mg CaCO₃/L, no detrimental effect for either cladoceran was noted. The EC₅₀ based on progeny was 38 mg CaCO₃/L forC. dubia and 5 mg CaCO₃/L forD. magna. This indicated thatD. magna is more tolerant of low levels of hardness than isC. dubia. When selecting test organisms for the biomonitoring of effluents such observations should be borne in mind.     

Long-Term Toxicity of Gadolinium to the Freshwater Crustacean Daphnia magna

The lanthanides are considered emerging contaminants but information on their long-term toxicity to aquatic species under environmentally relevant conditions is scarce. We aimed to fill this gap by evaluating the long-term adverse effects of gadolinium on the freshwater model—crustacean Daphnia magna. The exposure of D. magna for up to 39 days to 0.1 mg Gd/L (a 21-days chronic toxicity NOEC value derived by us formerly) in the lake water had no negative effect (p?>?0.05) on vitality, size and reproduction of parent animals as well as their offspring. Thus, assumingly the current Gd contamination levels of surface waters pose no hazard to aquatic crustaceans that in general are very sensitive to various pollutants. Moreover, presence of 0.1 mg Gd/L in the lake water even mitigated the long-term toxic effect of 0.2 mg Ni/L (studied as a model co-contaminant) to D. magna’s vitality and productivity.

     

Predicting the Toxicity of Substituted Phenols to Aquatic Species and Its Changes in the Stream and Effluent Waters

The changes in the acute toxicity of 16 phenols toward Selenastrum capricornutum and Daphnia magna were examined as a function of their physical/chemical properties. The results demonstrated that phenols with a higher octanol-water partition coefficient (K_ow) had a higher toxicity toward aquatic organisms. The toxicity of phenols was closely related to the log K_ow values, with correlation coefficients of 0.93 (except for the nitrophenols) and 0.89 for S. capricornutum and D. magna, respectively. The changes in the phenols toxicities in the site waters (i.e., stream and effluent waters) were investigated by calculating the water effect ratios (WER) from the results of the toxicity tests in the site waters using D. magna. The results showed that the degree of ionization for each phenolic compound was altered by the differences in the dissociation constant (pK_a), and the change in the toxicity could be predicted. Therefore, the WER should be considered when the toxicity of phenolic compounds is estimated in site waters. The quantitative structure-activity relationships (QSAR) study showed that the toxicity of the phenols to D. magna could be predicted by the hydrophobicity (log K_ow) alone and by combining the log K_ow with pK_a, while the toxicity to S. capricornutum was predicted by a combination of hydrophobicity (log K_ow) and E_LUMO (or pK_a).     

Toxicity of Chiral Pesticide <Emphasis Type="Italic">Rac-</Emphasis>Metalaxyl and <Emphasis Type="Italic">R-</Emphasis>Metalaxyl to <Emphasis Type="Italic">Daphnia magna</Emphasis>

Chirality in pesticides has become a challenge because of enantiomers’ different toxicities to non-target organisms. Acute and chronic toxicities of Rac-metalaxyl and R-metalaxyl to Daphnia magna were determined and compared. The 48-h LC50 for Rac- and R-metalaxyl to Daphnia magna were 51.5 and 41.9 mg/L. In a 14-day chronic test, the lowest-observed-effective concentration (LOEC) and no-observed-effective concentration (NOEC) of Rac-metalaxyl were 2 and 1 mg/L, respectively, whereas those of R-metalaxyl were 1 and 0.1 mg/L. Body length, days-to-first-brood and number of broods per female were significantly (p < 0.05) affected by R-metalaxyl at >1.0 mg/L, but affected by Rac-metalaxyl at ≥2.0 mg/L.     

Effects of the 1-alkyl-3-methylimidazolium bromide ionic liquids on the antioxidant defense system of Daphnia magna

This study examined the antioxidant responses of Daphnia magna following exposure to different concentrations of the ionic liquid (IL) 1-octyl-3-methylimidazolium bromide and the 50% LC₅₀ concentrations of methylimidazolium bromide ILs with different alkyl-chain lengths. Activities of antioxidant defense enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase) and levels of the antioxidant glutathione and the lipid peroxidation by-product malondialdehyde were measured using traditional methods or commercial kits. The concentration and the alkyl-chain length of ILs were found to strongly influence the antioxidant system of D. magna following IL exposure, and exposure to higher IL concentrations and to ILs with longer alkyl chains generally increased the enzyme activities and biomarker levels examined. Therefore, the present study suggests that oxidative stress is involved in the mechanism of IL-induced toxicity in D. magna.     

Toxicity of Select Beta Adrenergic Receptor-Blocking Pharmaceuticals (B-Blockers) on Aquatic Organisms

One class of pharmaceutical compounds identified in U.S. and European waters are the B-adrenergic receptor blocking compounds (B-blockers). However, little information is available on the potential aquatic toxicity of these compounds. Therefore, Hyalella azteca, Daphnia magna, Ceriodaphnia dubia, and Oryias latipes (Japanese medaka) were exposed to metoprolol, nadolol, and propranolol to determine potential toxicity. Average 48-h LC₅₀ for propranolol to H. azteca was 29.8 mg/L. The no-observed-effects concentration (NOEC) and lowest-observed-effects concentration (LOEC) for propranolol affecting reproduction of H. azteca were 0.001 and 0.1 mg/L, respectively. The average propranolol and metoprolol 48-h LC₅₀s for D. magna were 1.6 and 63.9 mg/L, respectively. C. dubia 48-h LC₅₀s were 0.85 and 8.8 mg/L for propranolol and metoprolol, respectively. The NOEC and LOEC of propranolol affecting reproduction in C. dubia were 0.125 and 0.25 mg/L, respectively. In O. latipes, the propranolol 48-h LC₅₀ was 24.3 mg/L. Medaka growth was decreased at 0.5 mg/L propranolol. A 2-week medaka reproductive study indicated significant changes in plasma steroid levels; however, no changes in the average number of eggs produced or number of viable eggs which hatched was observed. In a 4-week follow-up propranolol exposure, the total number of eggs produced by medaka and the number of viable eggs that hatched were decreased at concentrations as low as 0.5 μg/L. Based on this study and the expected aqueous environmental exposure levels, adverse effects of propranolol to invertebrate populations is unlikely; however, further reproductive studies are need to elucidate the risk to teleosts. Received: 14 August 2001/Accepted: 4 March 2002     

Acute and chronic aquatic toxicity of ammonium perfluorooctanoate (APFO) to freshwater organisms

Recent concerns have been raised concerning the widespread distribution of perfluorinated compounds in environmental matrices and biota. The compounds of interest include ammonium perfluorooctanoate (APFO, the ammonium salt of perfluorooctanoic acid, PFOA). APFO is used primarily as a processing aid in the production of fluoropolymers and fluoroelastomers. The environmental presence of perfluorooctanoate (PFO⁻, the anion of APFO) and its entry into the environment as APFO make quality aquatic toxicity data necessary to assess the aquatic hazard and risk of APFO. We conducted acute and chronic freshwater aquatic toxicity studies with algae, Pseudokirchneriella subcapitata, the water flea, Daphnia magna, and embryo-larval rainbow trout, Oncorhynchus mykiss, using OECD test guidelines and a single, well-characterized sample of APFO. Acute 48–96 h LC/EC₅₀ values were greater than 400 mg/l APFO and the lowest chronic NOEC was 12.5 mg/l for inhibition of the growth rate and biomass of the freshwater alga. Un-ionized ammonia was calculated to be a potential significant contributor to the observed toxicity of APFO. Based on environmental concentrations of PFO⁻ from various aquatic ecosystems, the PNEC value from this study, and unionized ammonia contributions to observed toxicity, APFO demonstrates little or no risk for acute or chronic toxicity to freshwater and marine aquatic organisms at relevant environmental concentrations.     

Evaluation of a High-Hardness COMBO Medium and Frozen Algae forDaphnia magna

A new high-hardness (H-H) COMBO medium for long-term culturing and bioassay testing ofDaphnia magnawas evaluated in 21-day survival, growth, and reproduction studies. The COMBO medium originally designed for softwater daphnid species (i.e.,D. pulicaria) was modified for the hardwater speciesD. magna. This medium also allowed continuous culturing of a green algal food source for daphnids,Ankistrodesmus falcatus. After 12 generations of culturing in H-H COMBO medium, the mean fecundity was 128±12 (coefficient of variation=9.4%). No significant observations of dead young, aborted eggs, or reduced antennas were made during the 6 months of continuous culturing. The no-observable-effect concentration (NOEC) for a reference toxicant standard, 3,4-dichloroaniline (3,4-DCA), was 8.3 μg/liter, which is similar to published values. These studies demonstrate that H-H COMBO is an acceptable medium for use for culturing and bioassay testing withD. magna.. Additional experiments using frozen aliquots ofA. falcatuswere conducted. Although mean fecundity (64±7) and adult length were significantly decreased from the values for daphnids fed fresh algae, the NOEC for 3,4-DCA was >25 μg/liter. The use of this alternative food source in bioassay testing appears promising, but further optimization of feeding rates is warranted.     

A comparative study of genotype sensitivity to acute toxic stress using clones of Daphnia magna straus

The genetic typing of laboratory strains of Daphnia magna revealed that although there are genetic differences between different testing laboratory strains, most laboratories culture single genotypes as clones. A comparative study was made of the performance of five of the more common clones in terms of neonate mortality under acute exposure to nine toxic chemicals. The range in clonal EC₅₀ response was from less than one to more than two orders of magnitude in terms of concentration. Surprisingly, there was little pattern in rank order of response of clones exposed to different toxicants, thus suggesting that genotype-environment interactions were predominating. Nevertheless, it was suggested that specifying the genotype used in D. magna toxicity tests will result in increased test repeatability. Evidence indicating that culture environment may also significantly affect the performance of neonates in acute toxicity tests was also presented.     

Acute toxicity studies of surfactants toDaphnia magna andDaphnia pulex

Several experiments were designed to examine the acute toxicity of surfactants toDaphnia. Specific tests were designed to develop comparisons between existing acute toxicity data for fish and similar data forDaphnia, and to provide data on the effects of various environmental factors on resultant toxicity of surfactants toDaphnia. Acute toxicity data for a series of homologous linear alkyl benzene sulfonates (LAS) demonstrate increases of up to one order of magnitude in toxicity for each increase of two alkyl carbons. LC 50's obtained withDaphnia magna are similar to those obtained with bluegills,L. Macrochirus. Comparative tests withD. magna andD. pulex indicate no statistical differences in 48-hr LC 50 values for three anionic and two nonionic surfactants. A 50 mg/L concentration of suspended, naturally-occurring kaolin significantly reduced the toxicity of longer chain length LAS homologs and had no effect on nonionic surfactant toxicity.In tests with variable hardness concentrations, the acute toxicity of LAS toD. magna is a combined function of both culture and test water hardness. The toxicity of a nonionic surfactant toD. magna was higher in soft water and was not affected by culture water hardness levels.Unlike previously published data for fish, the results of acute toxicity tests withD. magna cultures previously exposed to 0.4 mg/L LAS for periods up to seven generations indicated no significant difference in LAS susceptibility compared to simultaneously tested unexposed controls.     

Microcosm Evaluation of the Toxicity and Risk to Aquatic Macrophytes from Perfluorooctane Sulfonic Acid

Perfluorooctane sulfonic acid (PFOS) is an anthropogenic contaminant detected in various environmental and biologic matrices. This compound is a fluorinated surfactant, a class of molecules renowned for their persistence and their global distribution but for which few ecotoxicological data are currently available, especially under field conditions. The toxicity of PFOS to the aquatic macrophytes Myriophyllum sibiricum and M. spicatum was investigated using 12,000 L outdoor microcosms. Replicate microcosms (n=3) were treated with 0.3, 3, 10, and 30 mg/L PFOS as the potassium salt and assessed at regular intervals during a period of 42 days. M. sibiricum was more sensitive to PFOS under these simulated field conditions than M. spicatum. Toxicity was observed in the evaluated end points at >3 mg/L PFOS for EC₁₀s and >12 mg/L PFOS for EC₅₀s for M. spicatum and in M. sibiricum at >0.1 mg/L PFOS for EC₁₀s and >1.6 mg/L PFOS for EC₅₀s. The no observed–effect concentration (NOEC) for M. spicatum was consistently 11.4 mg/L PFOS, whereas the NOEC for M. sibiricum was 0.3 mg/L PFOS. A risk assessment for these plants estimated a negligible probability of toxicity being observed in these plants from PFOS exposure at current environmental concentrations.     

Salinity Tolerance of Daphnia magna and Potential Use for Estuarine Sediment Toxicity Tests

Daphnia magna Straus, a common organism used for freshwater sediment toxicity tests, was evaluated to determine its tolerance to salinity and suitability for tests with estuarine water and sediments. Daphnids were exposed for 2 to 21 days to salinity in a variety of water-only tests, in tests with freshwater sediment overlain by salt water, and in tests with estuarine sediments overlain by freshwater. Daphnid age, test length, and temperature seemed to have little effect upon the range of LC50, NOAEL, and LOAEL values. LC50s for all tests ranged from 5.10 to 7.81 g/L, with a mean of 6.6 g/L salinity (measured conductivity 10.0 mS/m). The mean NOAEL and LOAEL values based on production of young were 4.6 and 6.9 g/L salinity (measured conductivity 7.1 and 10.5 mS/m), respectively. The results indicate that D. magna will survive and reproduce well in water with salinities below 4 g/L and demonstrate the potential usefulness of this organism in monitoring sediment toxicity from both freshwater and estuarine wetland sites. Received: 26 September 1996/Revised: 21 November 1996     

Toxicity and Bioconcentration Potential of the Agricultural Pesticide Endosulfan in Phytoplankton and Zooplankton

Agricultural pesticide runoff in southeastern coastal regions of the United States is a critical issue. Bioconcentration of pesticides by phytoplankton and zooplankton at the base of the aquatic food web may increase the persistence of pesticides in aquatic ecosystems and cause effects at higher trophic levels. This study examined the toxicity of a widely used agricultural pesticide, endosulfan, to Pseudokirchneriella subcapitatum (freshwater green alga) and Daphnia magna (freshwater cladoceran). We then investigated the potential of both plankton species to sequester endosulfan from their surrounding media. We also assessed the degree to which endosulfan is accumulated by D. magna via food (endosulfan-contaminated P. subcapitatum). A 96-h growth rate EC₅₀ of 427.80 μg/L endosulfan was determined for P. subcapitatum, whereas a 24-h immobilization EC₅₀ of 366.33 μg/L endosulfan was determined for D. magna. The 5-h EC₅₀s for filtration and ingestion in D. magna were 165.57 μg/L and 166.44 μg/L, respectively. An average bioconcentration factor (BCF) of 2,682 was determined for P. subcapitatum exposed to 100 μg/L endosulfan for 16 h. An average BCF of 3,278 was determined for D. magna in a 100 μg/L endosulfan water-only exposure. There was negligible uptake of endosulfan by D. magna feeding on contaminated algae in clean water (BCF ∼ 0). Different proportions of parent isomers (endosulfan I and II) and the primary degradation product (endosulfan sulfate) were detected among treatments. Endosulfan was rapidly accumulated and concentrated from water by P. subcapitatum and D. magna neonates. Endosulfan contained in phytoplankton, however, was not bioaccumulated by zooplankton. These findings may prove useful in assessing ecosystem risk, because uptake from the water column appears to be the dominant route for bioconcentration of endosulfan by zooplankton. Received: 30 January 2001/Accepted: 26 August 2001     

The sensitivity of two cladocerans to water quality variables: Alkalinity

The sensitivity ofDaphnia magna andCeriodaphnia dubia to various levels of carbonate alkalinity and to the reference toxicant, NaCl, were examined in reconstituted water using the three brood test.D. magna was more tolerant of high levels of alkalinity and NaCl than wasC. dubia. The LC₅₀, based on survival at the end of the three brood test was 730 (592–1006) mg CaCO₃/L and 4205 (3415–5174) NaCl/L forD. magna and 237 (183–306) mg CaCO₃/L and 2160 (1296–3000) NaCl/L forC. dubia. No statistically significant effect of low levels of alkalinity could be discerned for either cladoceran. EC₅₀ values were calculated for total progeny, number of broods and the average brood size. The most sensitive endpoint forD. magna was the EC₅₀ based on total progeny for both alkalinity 416 (0–1076) mg CaCO₃/L and salinity 4181 (58–8306) mg NaCl/L. The most sensitive endpoint forC. dubia was the EC₅₀ based on total progeny 272 (20–524) mg CaCO₃/L and average brood size 273 (26–521) mg CaCO₃/L, the figure being the same for both parameters for alkalinity. In the case of salinity, the most sensitive endpoint forC. dubia was based on average brood size 1679 (5–3353) mg NaCl/L. As the brood number progresses from one to five,C. dubia exhibited enhancements of the mean brood size relative to that of the controls suggesting a chronic effect from higher levels of alkalinity. This observation was not noted inD. magna broods. A discussion is provided on measurements of carbonate alkalinity and related problems.     

Acute and Chronic Toxicity of Buprofezin on <Emphasis Type="Italic">Daphnia Magna</Emphasis> and the Recovery Evaluation

The toxic effects of buprofezin on Daphnia magna after both chronic and acute exposures were evaluated according to OECD guidelines. A 48-h acute exposure of buprofezin resulted in daphnid immobility at an EC₅₀ of 0.44 mg/L. In a 14 days chronic exposure of buprofezin (0, 0.025, 0.05, 0.10 and 0.15 mg/L), the development and reproduction of daphnids were all significantly affected and the body length was more sensitive than other observed parameters. However, the adverse effects of buprofezin on parental daphnids can be passed on to their offspring and cannot be recovered in a short time.     

The toxicity of waterborne boron toDaphnia magna andChironomus decorus and the effects of water hardness and sulfate on boron toxicity

The concentrations of many elements, including boron, are increasing in aquatic ecosystems due to anthropogenic activities. Laboratory studies were undertaken to evaluate the toxicity of waterborne boron to two key fresh water macroinvertebrates and to evaluate the effects of water hardness and sulfate on boron toxicity. Acute toxicity evaluations of waterborne sodium tetraborate resulted in 48 h. LC₅₀ values of 141 and 1376 mg B/L for neonateDaphnia magna and fourth instarChironomus decorus, respectively. Chronic sublethal studies demonstrated a significant decrease inC. decorus growth rate at 20 mg B/L. Further studies showed that increasing water hardness (10.6 to 170 mg/L as CaCO₃) and sulfate (10.2 to 325.4 mg SO₄ ^–1/L) concentrations did not affect boron toxicity toD. magna. These results, in conjunction with a review of the literature, suggest that aquatic macrophytes may be more sensitive to boron than macroinvertebrates and thus would be better choices for aquatic risk assessment evaluations for this element.     

Acute and chronic toxicity of 2,3,4,6-tetrachlorophenol and pentachlorophenol to Daphnia and rotifers

The toxicities of 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (PCP) were determined in standardized, single-species laboratory toxicity tests using daphnids and rotifers. For Daphnia magna, 48-h LC50 estimates with neonates indicated that PCP was more toxic than TeCP. The commercial TeCP formulation DIATOX^®, containing a 6.5:1 ratio of TeCP:PCP, exhibited intermediate toxicity. Mean LC50 estimates were 1.23, 2.66, and 2.07 mg/L, respectively. All three LC50 estimates were significantly different (p<0.05). Daphnia galeata mendotae was more sensitive to TeCP than D. magna displaying a mean 48-h LC50 value of 0.58 mg/L. A 21-d partial life cycle test with D. magna revealed no effects at 0.25 mg/L TeCP, but a significant (p<0.05) increase in adult mortality was noted at 0.50 mg/L TeCP. There was no effect on reproductive success of surviving adults at any test concentration.Rotifer tests, conducted with a commercially available species (Brachionus calyciflorus) and a field collected species (Keratella cochlearis), also indicated that PCP was more acutely toxic than TeCP. LC50 estimates for B. calyciflorus were highly variable depending upon the source of resting eggs (cysts) and the test conditions. LC50 estimates (24-h) ranged from 2.09 to 7.76 mg/L for PCP and from 2.31 to >16.00 mg/L for TeCP. In general, B. calyciflorus was less sensitive to TeCP and PCP than D. magna and D. g. mendotae. Assays with K. cochlearis were only marginally successful, but the mean 12-h LC50 estimate for TeCP of 0.96 mg/L suggested that this species may be more sensitive to TeCP than B. calyciflorus.