Influence of an insect growth regulator on the larval development of an estuarine shrimp

The influence of methoprene, an insect growth regulator used in mosquito control, on larval development of the estuarine grass shrimp (Palaemonetes pugio) was examined in the laboratory. No grass shrimp larvae successfully completed metamorphosis when continuously exposed to 1000 microg methoprene litre(-1). Completion of larval metamorphosis was significantly reduced by exposure to 100 microg litre(-1) of the isomeric mixture (R,S)-methoprene but not the single isomer formulation (S)-methoprene. No statistically significant difference was revealed, however, in ability to inhibit metamorphosis between these two isomeric types across the broad range of exposure concentrations from 0.1 to 1000.0 microg litre(-1). The first two larval stages and the final premetamorphic larval stage were more sensitive to methoprene toxicity than intermediate larval stages. Methoprene exposure did not alter either the duration of total larval development or the total number of larval stages prior to metamorphosis.     

The influence of an insect growth regulator on the larval development of the mud crab Rhithropanopeus harrisii

Effects of the juvenile hormone analogue (S)-methoprene on the larval development and survival of the estuarine mud crab Rhitrhopanopeus harrisii were examined in the laboratory. Crab leave continuously exposed to 1000 microg (S)-methoprene litre(-1) did not survive beyond zoeal stage I. With continuous exposure to 100 microg (S)-methoprene litre(-1), mortality significantly increased through all larval stages except for zoeal stage II, and developmental duration significantly increased through all zoeal stages but not the premetamorphic megalopa. No supernumerary larval stages occurred with exposure (S)-methoprene. Rhithropanopeus harrisii larvae appear to be more sensitive to the single isomer formulation, (S)-methophrene, than to the double isomer formulation, (S)-methoprene, used in previously documented studies.     

Chronic effects of Cd on reproduction of Polypedilum nubifer (Chironomidae) through water and food

Chronic effects of Cd on reproduction of Polypedilum nubifer (Chironomidae) were investigated by Cd-exposure from the egg stage using a flow-through aquarium. No significant effect of Cd on reproduction was observed in the midge larvae which had been exposed to 10 or 20 microg Cd litre(-1). Emergence of the Cd-exposed larvae peaked several days before that of the control, although growth was impaired in 1st and/or 2nd instars. The percentage emergence success decreased to about 46% of the control at 40 microg Cd litre(-1). However, other reproductive processes (adult sex ratio, oviposition success and egg hatchability) were not impaired. The emergence success decreased to less than 3% of the control at 80 microg Cd litre(-1). The emergence success of midge larvae which had been fed Cd-contaminated food with 220 or 1800 microg Cd g(-1) decreased to nearly 60% of the control. However, other reproductive processes were not impaired. Emergence success of larvae exposed to food containing 22 microg Cd g(-1) was unaffected.     

Toxicity of acid-sulphate soil leachate and aluminium to the embryos and larvae of Australian bass (Macquaria novemaculeata) in estuarine water

The toxicity of leachate water from acid-sulphate soil to the early life stages of Australian bass, Macquaria novemaculeata, incubated in seawater was evaluated. Acid-sulphate soil leachate water (pH> or =6.8) delayed the hatching of fertilised eggs, but after 48 h the per cent hatching was normal. In comparison, acidic saline water (25 per thousand salinity) at pH 4.0 or less prevented embryos from hatching. The survival of yolk-sac larvae exposed to acid-sulphate soil leachate water at a concentration of 32% in seawater and an initial pH of 7.2, was significantly different to controls after 96 hours. In corresponding tests with only acidified saline water (20 per thousand salinity), pH levels equal to or below 5.0 killed yolk-sac larvae after 96 h exposure. Aluminum showed a pH dependent toxicity to yolk-sac larvae, with added aluminium as low as 200 microg litre(-1) having a significant effect on larval survival at pH 5.5, and concentrations of 600-800 microg litre(-1) having a significant effect on larval survival at an initial pH range of 6.0 < pH < 6.8. It was concluded that significant mortality of the early life stages of Australian bass would occur if they are exposed to acid-sulphate soil leachate that results in a pH in the receiving estuarine water below 5.5, or when the pH is below 6.8 and aluminium is present at a total concentration of 800 microg litre(-1) or greater.     

Acute and chronic toxicity of triphenyltin hydroxide to fathead minnows (Pimephales promelas) following brief or continuous exposure

Fathead minnow larvae (Pimephales promelas) were exposed to triphenyltin hydroxide (TPTH) during brief (single pulse) or continuous exposure in 96-h and 30-day toxicity tests. The continuous exposure 96-h LC(50) value was 7.1 microg litre(-1). Brief exposures for 12 to 72-h gave 96-h LC(50) values that ranged from 61.8 to 6.0 microg litre(-1), respectively. The continuous exposure 30-day chronic effect concentration, based upon reduced growth, was 0.23 microg litre. Survival was significantly reduced at 2.0 microg litre(-1). Brief exposures for 24, 48, and 72-h in 30-day tests significantly reduced survival and growth at 13.0, 13.0 and 60.0 microg litre(-1) respectively. It is suggested that both toxicant concentration and exposure duration are important factors to consider in the risk assessment of potential pesticide hazards in the environment.     

Bioaccumulation of cadmium by the freshwater isopod Asellus aquaticus (L.) from aqueous and dietary sources

Experiments were conducted to determine the kinetics and relative importance of aqueous and dietary uptake of cadmium by the freshwater isopod Asellus aquaticus (L.). Test animals were exposed during 30 days to aqueous Cd in a continuous flow system (exposure levels: 0.2 - 10 microg litre(-1)) and kept on a diet of previously contaminated Elodea sp. (range of Cd concentrations: 2-350 microg g(-1), dry weight). Preceding semi-static experiments on dosage-control of the dietary factor revealed a rapid uptake of Cd by Elodea, with relatively high concentration factors (CF), which ranged from 4.8 to 5.5 (dry weight log (CF) after 16 days). For Asellus uptake from water appeared to be the predominant route. Highly significant bioconcentration of cadmium from water was observed in the animals, even at exposure levels below 1.0 microg litre(-1). In the various treatments, direct uptake from water accounted for 50-98% of the body burdens after 30 days exposure. The experimental results were described with a first order one-compartment bioaccumulation model. Model parameter estimates (mean +/- standard error) were obtained for rate constant of uptake (560 +/- 110 day(-1)), rate constant of elimination (0.032 +/- 0.017 day(-1)) and assimilation efficiency of Cd uptake from food (1.1 +/- 0.7%). The (dry weight) bioconcentration factor (BCF) and bioaccumulation factor (BAF) for extrapolated steady state conditions were estimated at 18 000 (BCF) and 0.08 (BAF). Experiments conducted at two different pH levels (5.9 versus 7.6) revealed no significant effects of pH on the uptake of aqueous Cd by the isopods. The results are discussed in relation to their potential significance to the field situation.     

An assessment of the chronic toxicity of the synthetic pyrethroid, fenvalerate, to Daphnia galeata mendotae, using life tables

The effects of chronic exposure to fenvalerate, a synthetic pyrethroid insecticide, on the cladoceran Daphnia galeata mendotae were evaluated under laboratory conditions. The daphnids were exposed for their entire life cycle to concentrations ranging from 0.005 to 0.1 microg fenvalerate litre(-1). The parameters used to determined toxicity were survival, time to first reproduction, reproductive frequency, number of young per brood, cumulative brood size, intrinsic rate of natural increase (r(m)), generation time (T) and net reproductive rate (R(0)). A concentration of 0.005 microg fenvalerate litre(-1) resulted in an increase in longevity but a decrease in production of young. Higher concentrations caused a decrease in survival. Studies of shorter duration than the complete life cycle of the organisms would not have detected toxicity at such low levels. The intrinsic rate of natural increase, r(m), was not affected by fenvalerate until concentration reached 0.05 microg litre(-1) and r(m) decreased to 0.113 from 0.238. A concentration of 0.01 microg litre(-1) caused the net reproductive rate, R(0), and the generation time, T, to decrease to 73.2 offspring per female and 17.3 days from 125.9 offspring per female and 20.3 days, respectively.     

Effects of different food (Chlorella) concentrations on the chronic toxicity of cadmium to survivorship, growth and reproduction of Echinisca triserialis (Crustacea: Cladocera)

Extraneous factors have been shown to greatly modify pollutant stress. The present study was conducted with the objective of determining whether differences in food levels could modify chronic toxicity of cadmium to the various life-history parameters of the cladoceran Echinisca triserialis. Laboratory experiments were conducted on a sublethal range of cadmium (0, 2.5, 5.0, 10 and 20 microg litre(-1)) on life-history parameters such as survivorship, longevity, life expectancy, age at first reproduction, total fecundity, neonate size, net reproductive rate (R0), generation time (T), intrinsic rate of natural increase (r) and growth of Echinisca triserialis in relation to different food (Chlorella) levels of 0.5 (low), 1.5 (medium) and 4.5 (high) x 10(6) cells ml(-1). Cadmium levels of 10 microg litre(-1) and above, and low food levels, had a profound effect in decreasing the magnitude of all parameters studied. EC50 levels computed for life-history parameters, such as longevity, life expectancy at birth, total fecundity, R0 and T, were in the range of 2 to 21 microg litre(-1) cadmium, and this is indicative of extreme adverse effects on the population dynamics of E. triserialis when exposed to low food levels. At high food levels the EC50 was not achieved for cadmium in the toxicant range studied. The significance of these results is discussed in relation to field conditions.     

Toxicity of fenvalerate to caddisfly larvae: chronic effects of 1- vs 10-h pulse-exposure with constant doses

Episodic pollution events such as runoff or spraydrift can lead to a short-term (few hours) contamination of aquatic ecosystems with pesticides. So far, different short-term exposures with respect to long-term effects have not been studied. In the present study, caddisfly larvae, typical for agricultural streams (Limnephilus lunatus Curtis, 2nd and 3rd instar) were exposed for 1- vs 10-h to three different equivalent doses (microg h) of fenvalerate. After transfer into an artificial stream microcosm with pesticide-free water, chronic effects were observed over 240 days. Comparison of 1- and 10-h exposure revealed that 1-h contamination leads to stronger effects. The differences were significant for the sublethal endpoints emergence pattern and dry weight of adults (ANOVA, Fisher's PLSD; P < 0.05). In terms of exposure dose, the difference between 1- and 10-h exposure equals a factor of 6 as a mean of all endpoints studied. The following significant effect levels for the 1-h exposure were obtained for the different endpoints investigated: reduced emergence success and production at 0.1 microg l(-1), temporal pattern of emergence at 0.001 microg l(-1), dry weight of adults at 0.01 microg l(-1).     

Transfer and effects of cadmium in an experimental food chain involving the snail Helix aspersa and the predatory carabid beetle Chrysocarabus splendens

The transfer and the toxic effects of Cd were studied in an experimental food chain involving the snail Helix aspersa as prey organism and one of its natural predators, the carabid beetle Chrysocarabus splendens. Juvenile snails were fed plant-based food enriched with 0, 10, 50 and 100 microg g(-1) of Cd, then were offered as prey to beetle larvae from egg hatching to pupation stage. Cd concentrations in snail tissues increased with increasing Cd concentration in food and with duration of exposure. Bioaccumulation factors ranged from 1.87 to 3.39, showing that H. aspersa snails, even in their early life stages, belong to macroconcentrator species for Cd. No significant reduction of snail consumption by beetles was found in exposed groups. Cd concentrations in beetle larvae remained very low (lower than 1 microg g(-1) for all groups), demonstrating a very effective regulation capacity in beetle larvae. However, Cd concentrations in highest exposed groups were higher than those found in control groups. Cd contents in adult beetles were lower than in larvae, showing a loss of Cd during metamorphosis. Despite the low Cd concentrations found in beetles, their exposure to Cd contaminated snails led to 31% of mortality, which occurred only during pupation and for the highest exposure level. No clear sublethal effects were found. These results showed that snails inhabiting heavily polluted areas may represent a risk of secondary poisoning for predatory invertebrates and provided quantitative data on the transfer of Cd between two compartments of a terrestrial food chain.     

Short-term effects of metals on the filtration rate of the zebra mussel Dreissena polymorpha

In order to study the short-term ecotoxicity of metals to the freshwater mussel Dreissena polymorpha, the effects of Cu, Zn and Cd on the filtration rate of this mussel were determined in laboratory experiments. Filtration rate was chosen as the endpoint, because it is a sensitive sublethal parameter compared to mortality and it is an important parameter given the ecological role D. polymorpha fulfills. The filtration rate was calculated from the decrease in algal concentration, fed to mussels in aquaria, containing different metal concentrations. The EC50 for Cu (41 microg litre(-1)) was lower than for Cd (388 microg litre(-1)) and Zn (1350 microg litre(-1)). The NOEC(accumulation) for the essential metal Zn was higher than for the essential metal Cu. Cadmium, a non-essential metal, was accumulated at all elevated water concentrations, so the NOEC(accumulation) was the concentration in the control water (<0.2 microg litre(-1)). All (no) effect concentrations found in this study were above the quality criteria set for metal concentrations in Dutch surface water, suggesting that the zebra mussel is sufficiently protected by these quality criteria.     

Effects of repeated application of carbaryl on zooplankton communities in experimental ponds with or without the predator Chaoborus

Zooplankton communities with or without Chaoborus larvae were established in outdoor experimental ponds, to which the insecticide carbaryl was applied repeatedly at 10 or 100 microg litre(-1). In the ponds without Chaoborus, Cladocera dominated, but the species composition differed among the treatments. A large-sized Cladocera Daphnia galeata dominated the controls, the medium-sized cladocerans Diaphanosoma brachyurum and Moina micrura became dominant in the low-dose treatment, and the small-sized Bosmina fatalis increased in the high-dose treatment. These results indicated differential sensitivity to carbaryl among the cladocerans, and that smaller Cladocera were more tolerant of the chemical than the larger one. In the ponds with Chaoborus, rotifers dominated the zooplankton, probably because Chaoborus released rotifers from competition with cladocerans and calanoid copepods, which were eliminated by the Chaoborus predation. No effects of low-dose carbaryl treatment were detected on zooplankton communities in the Chaoborus ponds. The dominance by rotifers, organisms tolerant to carbaryl, minimized the effects. Thus, Chaoborus altered the zooplankton community responses to the chemical application by changing community structure. Repeated application of high-dose carbaryl did affect the rotifer community, decreasing the dominance of Polyarthra trigla and increasing that of Keratella valga. These rotifer species may differ in their sensitivity to carbaryl.     

Unavailability of polynuclear aromatic hydrocarbons from coal particles to the eastern oyster

The accumulation by oysters of polycyclic aromatic hydrocarbons (PAH) from coal dust entering the estuarine environment has been postulated in the vicinity of coal transfer operations. Oysters Crassostrea virginica were exposed to coal dust plus 15 day leachate at concentrations of 10 mg litre(-1) and 1 mg litre(-1) coal dust for 28 days in a flow-through test system. Potential effects of the exposures were measured by comparing the uptake of PAH and the growth of the exposed animals versus control groups. Oysters sampled at 7, 14 and 28 days did not exhibit an increase in PAH body burden over control animals provided the guts were first purged of particulates. Even at the high test concentrations (10 mg litre(-1)), no effect of the exposure on shell growth was observed.     

The induction of metallothionein in tissues of the Norway lobster Nephrops norvegicus following exposure to cadmium, copper and zinc: the relationships between metallothionein and the metals

Nephrops norvegicus were exposed simultaneously to cadmium, copper and zinc over an 18-day period. Exposure concentrations were control, 1, 5 and 25 microg litre(-1) for cadmium and copper and 8, 40 and 200 microg litre(-1) for zinc. Concentrations of cadmium, copper, zinc and metallothionein were measured in homogenates of both the gill and the hepatopancreas. Quantification of metallothionein was carried out by differential pulse polarography. Cadmium concentrations increased significantly in the gill and hepatopancreas of both male and female animals in response to increases in exposure concentration. In contrast, the concentration of copper and zinc increased significantly in the gills of males, but not in females. In the hepatopancreas, neither copper nor zinc resulted in significant changes in concentrations of these metals. Metallothionein concentrations in the gill and hepatopancreas were increased significantly in relation to metal exposure in both males and females. Concentrations of cadmium and metallothionein in both the gill and hepatopancreas of males and females were positively correlated. Copper in the hepatopancreas also showed positive relationships with MT concentrations in males, but not in females. This study suggested that cadmium MTs in the gill and hepatopancreas of Nephrops norvegicus could be used as a sensitive tool to detect cadmium contamination in the lobsters, although this was not true for copper and zinc.     

The mixing zone between limed and acidic river waters: complex aluminium chemistry and extreme toxicity for salmonids

When liming running waters, dosers must compensate for different flow and water qualities and for the downstream inflow from acid tributaries which creates mixing zones. At a certain point in the mixing zone, a constant or fluctuating chemical disequilibrium will appear due to transformation processes. In laboratory assays, over-saturated solutions of aluminium with ongoing active precipitation of aluminium have been found to be especially toxic to fish. Recent experiments in a mixing zone in the limed River Audna, Norway, have confirmed this phenomenon. Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) smolts were exposed to acid and limed waters and mixtures of the two waters downstream from the point of connection. In the acid tributary (mean values: pH=4.8, Ca=1.3 mg litre (-1)), Ali 236 microg litre(-1)=), LT5) was 22 and 40 h for Atlantic salmon and sea trout, respectively. In the mixing zone (pH=4.8-6.5, Ca=1.2-3.2 mg litre(-1), Ali=50-240 microg litre(-1)), LT50 was 7 h for both species, masking the normal species difference in tolerance. Osmoregulatory failure and rapid gill lesions occurred in the mixing zone as an effect of the transformation of Al into high molecular weight precipitating species. This is the first documentation of the existence of such highly toxic mixing zones in nature, and the results clearly show that the mixing zone is even more toxic to fish than acid aluminium-rich waters.     

Bioconcentration of trans-chlordane by the midge, Chironomus decorus

The accumulation and transport of the organochlorine pesticide, trans-chlordane, by the midge, Chironomus decorus was examined in a whole life cycle laboratory exposure assay. Larvae were kept in dosed water exposures including food particles from egg stages through adult metamorphosis and were sampled for weight gain and chemical content over the course of the 50 day study. Accumulation of trans-chlordane was related to the amount of contaminant in the larval environment. Concentration of trans-chlordane (ng contaminant/g tissue) in larvae was not significantly different from second through fourth instar stages but depended upon the weight of the larvae. Differences in time to metamorphosis, weight gain and sex ratios occurred among all replicate exposures, including controls, suggesting nongenetic maternal differences, rather than environmental variation caused by chemical exposure. When the larvae metamorphosed, an average of 82.6% of the contaminant was retained in the adults while 11.4% was left behind in the shed exuviae. This study suggests that terrestrial predators feeding on emerging aquatic insects can be exposed to organic pesticides from aquatic environments.     

Effects of formulations of the fungicide, pentachloronitrobenzene on early life stage development of the Japanese medaka (Oryzias latipes)

Quintozene is a fungicide containing the active ingredient, pentachloronitrobenzene (PCNB) that is used to control "snow mold" on golf courses in temperate regions of North America. In this study, quintozene and a formulation of quintozene widely used on golf courses, FFII were tested for toxicity to early life stages of the Japanese medaka, Oryzias latipes. For medaka exposed in static non-renewal assays to quintozene for 17d from the fertilized egg stage to yolk resorption at the fry stage, the LC(50) for mortality was a nominal concentration of 707 microgl(-1) and the effective concentration for 50% hatch (i.e. EC(50)) was a nominal concentration of 71 microgl(-1). Eggs and fry showed developmental abnormalities, including ocular malformations and retarded development of the brain, notochord, organs and body segmentation, which were interpreted as teratogenic responses to exposure to PCNB. For medaka exposed to quintozene, the LOECs for abnormalities of the eye and all other developmental abnormalities were 750 and 100 microgl(-1), respectively. In medaka exposed to the FFII formulation, similar patterns of mortalities, reduced hatching success and developmental abnormalities were observed, but at higher test concentrations that were consistent with the proportion of quintozene in the formulation. For medaka exposed to the formulation, the LOECs for abnormalities of the eye and all other developmental abnormalities were 10,000 and 1,000microgl(-1), respectively. Overall, these data indicate that studies should be conducted to assess the risk of exposure of early life stages of fish to quintozene in watersheds impacted by golf courses.     

Effects of fenoxycarb exposure on complete larval development of the xanthid crab,Rhithropanopeus harrisii

Pest control agents, such as juvenile hormone analogues (JHA), have been developed to limit effects on non-target organisms that co-inhabit insect pest habitats. Rhithropanopeus harrisii, an estuarine xanthid crab, was used to observe the impacts of the JHA, fenoxycarb, on the pattern of complete larval development as well as survival of larvae and successful metamorphosis to first crab stage. Significant mortality occurred in the first of four zoeal stages (after 2-3 days of exposure) at the highest treatment of 240 microg fenoxycarb/l and in megalopae exposed to 48 microg fenoxycarb/l. The time required to metamorphose to the first crab stage was significantly increased for megalopae in all treatments 48 microg/l. This delay in development was sufficient to significantly prolong the entire developmental period from zoea to crabs. Unexposed larvae developed to crabs in an average of 16 days; larvae exposed to >/=48 microg/l required 19-20 days. Reduced survival and extended duration of developing larval stages in the life history of a benthic invertebrate may alter the population dynamics of these organisms in the estuary.     

Effects of lead-contaminated surface water from a trap and skeet range on frog hatching and development

Pickerel frogs (Rana palustris) and bullfrogs (Rana catesbeiana) were exposed from the egg stage to lead-contaminated surface water from a trap and skeet range. Seven experimental treatments were employed: 25, 50, 75 and 100% range water, 100% range water plus a chelating agent (sodium citrate), control water and control water plus chelating agent. Total lead concentrations in 100% range water treatments varied from 840-3150 microg litre(-1), with the filterable form accounting for approximately 4-5% of the total. Hatching was not affected in either species (p > 0.2). There were highly significant differences in mortality among treatments for R. palustris (p = 0.0001), with tadpoles exhibiting 100 and 98% mortality after 10 d of exposure to 100 and 75% range water, respectively. Mortality in the 100% range water + citrate treatment was similar to controls (p > 0.05). There were no significant differences in mortality among treatments for R. catesbeiana after 10 d of exposure (p = 0.7119). Exposure to lead in the range water did not adversely affect the growth of surviving R. palustris or R. catesbeiana tadpoles after 14 weeks and 10 weeks, respectively. In both species, the intestinal mucosa in tadpoles exposed to range water was reduced in thickness. Scanning electron micrographs of R. palustris tadpoles that died in 100% range water revealed stunted tail growth, incurvation of the spine, hydropsy and generally reduced body size.     

Developmental toxicity and stress protein responses in zebrafish embryos after exposure to diclofenac and its solvent, DMSO

One of the most frequently detected pharmaceuticals in environmental water samples is the anti-rheumatic drug, diclofenac. Despite its increasing environmental significance, investigations concerning the effects of this drug on the early developmental stages of aquatic species are lacking up to now. To determine the developmental toxicity and proteotoxicity of this drug on the growing fish embryos, eggs of zebrafish were exposed to six concentrations of diclofenac (0, 1, 20, 100, 500, 1000, and 2000 microg l(-1)) using DMSO as solvent. Early life stage parameters such as egg and embryo mortality, gastrulation, somite formation, movement and tail detachment, pigmentation, heart beat, and hatching success were noted and described within 48- and 96-h of exposure. After the 96-h exposure, the levels of stress proteins (hsp 70) were determined in both the diclofenac-treated and respective DMSO controls. Results showed no significant inhibition in the normal development until the end of 96 h for all exposure groups. However, there was a delay in the hatching time among embryos exposed to 1000 and 2000 microg l(-1). Late-hatched embryos (108 h) did not differ morphologically from normally hatched embryos. The mortality and average heart rate data did not show significant differences for all embryos in both diclofenac-treated and DMSO control groups. No significant malformations were likewise noted among all developing embryos throughout the exposure period. The levels of heat shock proteins in diclofenac-treated and control embryos did not differ significantly. DMSO control embryos, on the other hand, showed a concentration-dependent increase in hsp 70 levels. We suggest possible modulating effect of diclofenac in DMSO-triggered expression of stress proteins and this might have a possible repercussion on the use of DMSO as solvent in any toxicity assay. Since the present data indicate no significant embryotoxicity and proteotoxicity induced by diclofenac and due to the fact that the concentrations of diclofenac used in the present study is up to 2000-fold higher than the concentrations detected in the environment, it is unlikely that this drug would pose a hazard to early-life stages of zebrafish.