Toxicity of Sediment-Associated Pesticides to <Emphasis Type="Italic">Chironomus dilutus</Emphasis> and <Emphasis Type="Italic">Hyalella azteca</Emphasis>

Two hundred sediment samples were collected and their toxicity evaluated to aquatic species in a previous study in the agriculturally dominated Central Valley of California, United States. Pyrethroid insecticides were the main contributors to the observed toxicity. However, mortality in approximately one third of the toxic samples could not be explained solely by the presence of pyrethroids in the matrices. Hundreds of pesticides are currently used in the Central Valley of California, but only a few dozen are analyzed in standard environmental monitoring. A significant amount of unexplained sediment toxicity may be due to pesticides that are in widespread use that but have not been routinely monitored in the environment, and even if some of them were, the concentrations harmful to aquatic organisms are unknown. In this study, toxicity thresholds for nine sediment-associated pesticides including abamectin, diazinon, dicofol, fenpropathrin, indoxacarb, methyl parathion, oxyfluorfen, propargite, and pyraclostrobin were established for two aquatic species, the midge Chironomus dilutus and the amphipod Hyalella azteca. For midges, the median lethal concentration (LC₅₀) of the pesticides ranged from 0.18 to 964 μg/g organic carbon (OC), with abamectin being the most toxic and propargite being the least toxic pesticide. A sublethal growth endpoint using average individual ash-free dry mass was also measured for the midges. The no–observable effect concentration values for growth ranged from 0.10 to 633 μg/g OC for the nine pesticides. For the amphipods, fenpropathrin was the most toxic, with an LC₅₀ of 1–2 μg/g OC. Abamectin, diazinon, and methyl parathion were all moderately toxic (LC₅₀s 2.8–26 μg/g OC). Dicofol, indoxacarb, oxyfluorfen, propargite, and pyraclostrobin were all relatively nontoxic, with LC₅₀s greater than the highest concentrations tested. The toxicity information collected in the present study will be helpful in decreasing the frequency of unexplained sediment toxicity in agricultural waterways.     

<Emphasis Type="Italic">Hyalella azteca</Emphasis> (Saussure) Responses to Coldwater River Backwater Sediments in Mississippi,USA

Sediment from three Coldwater River, Mississippi backwaters was examined using 28 day Hyalella azteca bioassays and chemical analyses for 33 pesticides, seven metals and seven PCB mixtures. Hydrologic connectivity between the main river channel and backwater varied widely among the three sites. Mortality occurred in the most highly connected backwater while growth impairment occurred in the other two. Precopulatory guarding behavior was not as sensitive as growth. Fourteen contaminants (seven metals, seven pesticides) were detected in sediments. Survival was associated with the organochlorine insecticide heptachlor.     

Acute and Chronic Toxicity of Imidacloprid to the Aquatic Invertebrates <Emphasis Type="Italic">Chironomus tentans</Emphasis> and <Emphasis Type="Italic">Hyalella azteca</Emphasis> under Constant- and Pulse-Exposure Conditions

The toxicity of imidacloprid, a nicotinic mimic insecticide, to the aquatic invertebrates Chironomus tentans and Hyalella azteca, was first evaluated in static 96-hour tests using both technical material (99.2% pure) and Admire, a commercially available formulated product (240 g a.i. L(-1)). The 96-h lethal concentration (LC)50 values for technical imidacloprid and Admire were 65.43 and 17.44 microg/L, respectively, for H. azteca, and 5.75 and 5.40 microg/L, respectively, for C. tentans. Admire was subsequently used in 28-day chronic tests with both species. Exposure scenarios consisted of a constant- and a pulse-exposure regime. The pulse exposure lasted for four days, after which time the animals were transferred to clean water for the remaining 24 days of the study. Assessments were made on both day 10 and day 28. In the C. tentans under constant exposure, larval growth on day 10 was significantly reduced at 3.57 microg/L imidacloprid, the lowest-observed-effect concentration (LOEC). The no-observed-effect concentration (NOEC) and LOEC for the 28-day exposure duration (adult survival and emergence) were 1.14 and greater than 1.14 mug/L, respectively; the associated LC50 and LC25 were 0.91 and 0.59 microg/L, respectively. The LOEC for the pulse treatment was greater than 3.47 microg/L, but the day 10 LC25 was 3.03 microg/L. In the H. azteca tests, the day 10 and 28 constant exposure, as well as the day 28 pulse exposure, LOEC (survival) values were similar at 11.95, 11.46, and 11.93 microg/L, respectively. The day 10 and 28 constant exposure effective concentration (EC)25s (dry weight) were also similar, at 6.22 and 8.72 microg/L, respectively, but were higher than the pulse-exposure day 10 LOEC and EC25 (dry weight) values of 3.53 and 2.22 microg/L, respectively. Overall, C. tentans was more sensitive to acute and chronic imidacloprid exposure, but less sensitive to a single pulse, than H. azteca. Chronic, low-level exposure to imidacloprid may therefore reduce invertebrate survival and growth, but organisms are able to recover from short-term pulse exposure to similar imidacloprid concentrations if the stressor is removed after four days.     

Effects of Copper in Flooded Florida Agricultural Soils on <Emphasis Type="Italic">Hyalella azteca</Emphasis>

This study examined the uptake and effects of copper (Cu) from flooded agricultural soils to epibenthic amphipods (Hyalella azteca) using 10-day sediment toxicity tests. Soils were collected from 10 citrus agricultural sites in South Florida. One sediment toxicity test was conducted with one flooding of the 10 soils, and based on the results of this test a second sediment toxicity test was conducted with 4 of the soils, after four 14-day flooding and four 14-day drying intervals over 4 months. Sediment toxicity tests were conducted under flow-through conditions using U.S. EPA methodology. Effects on survival, dry weight, and whole-body Cu concentrations of H. azteca were determined. Cu concentrations in overlying water and sediment of both sediment toxicity tests exceeded regulatory criteria for aquatic organisms. Although survival of H. azteca was not consistently affected from the first to the second sediment toxicity tests, dry weight was consistently reduced and related to Cu concentrations in soil, overlying water, and pore water. Furthermore, whole-body tissue Cu concentrations were significantly higher in H. azteca in all 10 soil-water treatments in the first sediment toxicity test and in all 4 soil-water treatments in the second sediment toxicity test compared to controls. Whole-body tissue concentrations and effects on dry weight were related to Cu exposures in soil, overlying water, and pore water. In these managed soil-water systems, small fish consuming H. azteca with high concentrations of Cu may be at risk.     

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.     

Impact of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide from Domestic Effluents on River Waters

The impacts of N,N-dimethylformamide (DMF) from domestic effluents on rivers were evaluated. The hourly DMF concentrations in the inflows (0.21–0.52 μg/L in mean) and the outflows (0.18–0.62 μg/L in mean) of two sewage treatment plants did not show any characteristic variations, and DMF was not removed at both plants. The monthly variations of DMF in the outflows of four sewage treatment plants (0.16–0.62 μg/L in mean) and three rivers (0.06–0.11 μg/L in mean) into which the outflows of the plants were discharged did not show any significant variations. The domestic DMF load per person was calculated to be 0.25 mg/d/person. The percent DMF loads of domestic effluents in the rivers were estimated to be below (8%–32%).     

Acute Toxicity of Methyl-Parathion in Wetland Mesocosms: Assessing the Influence of Aquatic Plants Using Laboratory Testing with <Emphasis Type="Italic">Hyalella azteca</Emphasis>

Methyl-parathion (MeP) was introduced into constructed wetlands for the purpose of assessing the importance of distance from the source of contamination and the role of emergent vegetation on the acute toxicity to Hyalella azteca (Crustacea: Amphipoda). A vegetated (90% cover: mainly Juncus effuses) and a nonvegetated wetland (each with a water body of 50 × 5.5 × 0.2 m) were each exposed to a simulated MeP storm runoff event. H. azteca was exposed for 48 h in the laboratory to water samples taken from the wetlands at a distance of 5, 10, 20, and 40 m from the pesticide inlet 3 h, 24 h, 96 h, and 10 days following application. Methyl-parathion was detected throughout the nonvegetated wetland, whereas the pesticide was only transported halfway through the vegetated wetland. A repeated-measure three-way analysis of variance (ANOVA) using time, location, and vegetation indicated significantly lower toxicity in the vegetated wetland. Furthermore, the mortality decreased significantly with both increasing distance from the inlet and time (48-h LC₅₀ ± 95% CI: 9.0 ± 0.3 g/L). A significant three-way interaction of time × vegetation × location confirmed higher toxicity at the inlet area of the nonvegetated wetland immediately after contamination. Significant linear regressions of maximum mortality (independent of time) versus distance from the pesticide inlet indicated that 44 m of vegetated and 111 m of nonvegetated wetland would reduce H. azteca mortality to 5%. These results suggest that vegetation contributes to reduced MeP effects in constructed wetlands.     

Effluent Toxicity Test Using Developmental Stages of the Marine Polychaete <Emphasis Type="Italic">Hydroides </Emphasis><Emphasis Type="Italic">elegans</Emphasis>

The US Environmental Protection Agency (USEPA) has established a suite of methods that use coastal invertebrate species as bioassay organisms to test industrial and domestic effluent as well as coastal waters for potential toxicity. Although these methods are used globally, the potential of such toxicity tests has not been adequately explored for Asian coastal waters. This study describes bioassay utilizing the gametes of Hydroides elegans to monitor coastal water quality and is based on the sensitivity of H. elegans embryo and larva to different concentrations of effluents and water samples collected from different regions of east coast of India. Among the water samples collected from different regions, seawater from Ennore station showed decrease in percentage of development, and 25% effluent concentration led to development arrest of H. elegans embryos. The different morphological effects produced by effluents clearly reflect the defect in early differentiation of embryonic cells. Since fertilization can be inhibited in the presence of any xenobiotic, both fertilization and early development can be used as a biological indicator for a rapid bioassay to monitor pollution. Toxicity tests utilizing early life stages of H. elegans are suitable for the assessment of effects produced by low levels of pollutants due to their high sensitivity to various contaminants relative to other marine species and also due to the relative simplicity of the bioassay.     

Effect of Nutrition on Toxicity of Contaminants to the Epibenthic Amphipod <Emphasis Type="Italic">Melita plumulosa</Emphasis>

The amphipod Melita plumulosa is commonly used to assess the toxicity of contaminated sediments. Seven-day-old M. plumulosa are <1 mm in size, and during 10-day tests in sandy sediments with low nutritional value, starvation can cause >50% mortality. In sediment toxicity tests, therefore, it can be difficult to determine if toxicity is due to contaminants or starvation, particularly in contaminated sandy sediments. This study investigated the influence of amphipod age and food addition on amphipod survival in toxicity tests. The 4-day LC₅₀ increased linearly from 120 to 470 μg/L when M. plumulosa age at the beginning of the test increased from 5 to 30 days. The addition of food as algae or fish food did not significantly affect the sensitivity of 11-day-old M. plumulosa (11-d Mp) to dissolved copper over 4 days in water-only tests. The survival of 11-d Mp in water-only tests over 10 days was poor without feeding, but when fed fish food, the 10-day LC₅₀ was 76 ± 15 μg/L. In sediment tests, feeding 0.063 mg fish food/amphipod on days 3 and 7 of 10-day tests consistently resulted in greater than 80% survival of 11-d Mp for a range of clean, sandy sediments, which had low amphipod survival without added food. Algae were not always suitable as a food source, as their growth can be stimulated by nutrients released from sediment and was inhibited by contaminants. The toxicity of most contaminated sediments was not ameliorated by the addition of food, suggesting that food addition was suitable for inclusion in routine testing protocols for this amphipod. An erratum to this article can be found at     

Effect of Nutrition on Toxicity of Contaminants to the Epibenthic Amphipod <Emphasis Type="Italic">Melita plumulosa</Emphasis>

The amphipod Melita plumulosa is commonly used to assess the toxicity of contaminated sediments. Seven-day-old M. plumulosa are <1 mm in size, and during 10-day tests in sandy sediments with low nutritional value, starvation can cause >50% mortality. In sediment toxicity tests, therefore, it can be difficult to determine if toxicity is due to contaminants or starvation, particularly in contaminated sandy sediments. This study investigated the influence of amphipod age and food addition on amphipod survival in toxicity tests. The 4-day LC₅₀ increased linearly from 120 to 470 μg/L when M. plumulosa age at the beginning of the test increased from 5 to 30 days. The addition of food as algae or fish food did not significantly affect the sensitivity of 11-day-old M. plumulosa (11-d Mp) to dissolved copper over 4 days in water-only tests. The survival of 11-d Mp in water-only tests over 10 days was poor without feeding, but when fed fish food, the 10-day LC₅₀ was 76 ± 15 μg/L. In sediment tests, feeding 0.063 mg fish food/amphipod on days 3 and 7 of 10-day tests consistently resulted in greater than 80% survival of 11-d Mp for a range of clean, sandy sediments, which had low amphipod survival without added food. Algae were not always suitable as a food source, as their growth can be stimulated by nutrients released from sediment and was inhibited by contaminants. The toxicity of most contaminated sediments was not ameliorated by the addition of food, suggesting that food addition was suitable for inclusion in routine testing protocols for this amphipod.     

Toxicity of Diclofenac in the Fern <Emphasis Type="Italic">Azolla filiculoides</Emphasis> and the Lichen <Emphasis Type="Italic">Xanthoria parietina</Emphasis>

This study investigated the occurrence of toxicity, expressed as damage to the photosynthetic apparatus, in the aquatic fern Azolla filiculoides and the lichen Xanthoria parietina following treatments with diclofenac at different concentrations (0.1, 1, 10 and 100 mg/L) and different exposure times (24, 48, 72 and 240 h). Measurements of photosynthetic efficiency, chlorophyll content and chlorophyll degradation indicated dose- and time-dependent toxicity, since significant differences with control samples as well as among treatments, emerged mainly for the highest concentration (100 mg/L) and the longest time (240 h). In addition, also the mycobiont of the lichen X. parietina showed similar toxic effects, expressed as ergosterol content. The absence of relevant alterations at the lowest concentration (0.1 mg/L) suggested a very limited susceptibility of these species to environmentally relevant levels of this pharmaceutical.     

Effects of Pentachlorophenol on <Emphasis Type="Italic">Galba pervia</Emphasis>, <Emphasis Type="Italic">Tubifex sinicus</Emphasis> and <Emphasis Type="Italic">Chironomus plumousus</Emphasis> Larvae

The 24-h median lethal concentrations of pentachlorophenol to Chironomus plumousus, Tubifex sinicus and Galba pervia were 0.302, 0.977 and 0.293 mg/L, respectively. Bioconcentration factors of C. plumousus, T. sinicus and G. pervia to pentachlorophenol were 108, 367 and 85 at 0.02 mg/L pentachlorophenol, respectively. As pentachlorophenol concentration increased, the G. pervia egg hatching rates became lower, and the total hatched time became longer. Pentachlorophenol teratogenesis was demonstrated by observing the deformation of C. plumousus larvae mentum.