Static Toxicity Tests Research Articles

Toxicity of trimethoprim towards marine microalgae: implication for environmental risk assessment

Context Trimethoprim (TMP) is a common antibacterial medication used in human and veterinary medicine, including in aquaculture. Antibiotic misuse and abuse results in the antibiotic pollution of water and has attracted increasing attention. Antibiotics are frequently detected in water bodies and pose a certain environmental risk to the aquatic system. Aims Two marine diatoms, i.e. Phaeodactylum tricornutum and Skeletonema costatum, were tested for toxicity to better understand the ecological implications of TMP in the marine system. Methods The routine static toxicity test method for microalgae was selected to be used. Key results The 96-h median effective concentration (EC50) values based on average specific growth rate (96-h ErC50) were >1.000 and >5.000 mg L−1 for P. tricornutum and S. costatum respectively. Conclusions P. tricornutum was more sensitive than S. costatum in its exposure to TMP, with a no observation-effect concentration (NOEC) value of 0.063 mg L−1. On the basis of the risk data, TMP poses a great risk to the aquatic system in certain countries. Implications The results of this study provide a better understanding of the potential ecological risks of TMP in the marine environment.

Uptake and depuration of water-soluble fractions (WSF) of crude oil by the bivalve Corbicula fluminea (Müller) from Shatt Al-Arab river

This study includes laboratory uptake and depuration experiments. The bivalve C. fluminea is exposed to 5ml of WSF of Nahran–Umar crude oil for each liter of river water for 48 hours in the static toxicity test system. The exposure water and animals are periodically taken for analysis of total hydrocarbons concentrations by spectroflurometer. After the exposure period is over, the bivalve transferred to clean river water for depuration period of 48 hours. The experiments show that there are no mortalities due to WSF of Nahran–Umar crude oil. The bivalve is usually active during the 12–16 hours of the experiments. Hydrocarbons concentrations in the exposure water decreased are slowly in a linear fashion so that no measurable concentrations remained after 32 hours. Hydrocarbons accumulated by the bivalve are slowly during the first few hours of exposure. After 2 hours of exposure, the concentration of hydrocarbons is approximately 0.38 ppm in water, while in tissues it is 4.8 ppm. After 20 hours, hydrocarbons are present in water at a concentration of 0.09ppm, while the bivalve tissues contained 17.7 ppm hydrocarbons. After 25 hours of exposure, the hydrocarbons concentration decreased in the bivalve tissues. At the end of the exposure period, the bivalve contains approximately 7.4 ppm. After 48 hours in clean river water, tissues burden decreased to 0.22 ppm of hydrocarbons. The bivalve remained contaminated with small concentrations of hydrocarbons for 20 days. The complete depuration occurred at 26 days.

Bioaccumulation of abacavir and efavirenz in Rhinella arenarum tadpoles after exposure to environmentally relevant concentrations

Antiretrovirals are pharmaceuticals used in the treatment of the human immunodeficiency virus; they are contaminants of emerging concern that have received considerable attention in recent decades due to their potential negative environmental effects. Data on the bioaccumulation and possible environmental risks posed by these drugs to aquatic organisms are very scarce. Therefore, the aim of this study was to evaluate the bioaccumulation of abacavir and efavirenz in Rhinella arenarum tadpoles subjected to acute static toxicity tests (96 h) at environmentally relevant concentrations. The analytical procedure consisted of the development and optimization of a method involving ultra-high performance liquid chromatography with tandem mass spectrometry detection. The instrumental conditions, optimized by design of experiments using the response surface methodology, yielded limits of detection of 0.3 μg L−1 for abacavir and 0.9 μg L−1 for efavirenz; and limits of quantification of 1.9 μg L−1 for abacavir and 5.6 μg L−1 for efavirenz. Subsequently, the bioaccumulation of the pharmaceutical drugs in tadpoles was evaluated at three exposure concentrations. Efavirenz displayed the highest bioaccumulation levels. This study shows the bioaccumulation potential of abacavir and efavirenz in amphibian tadpoles at exposure concentrations similar to those already detected in the environment, indicating an ecological risk for R. arenarum and probably other aquatic organisms exposed to these drugs in water bodies.

Water soluble fractions of crude oil deteriorates water quality parameters and alters histopathological components of juvenile Clarias gariepinus

In this study, the water quality changes after the introduction of water soluble fractions of crude oil were monitored along-side the accompanying effects on histopathological changes in selected organs of juvenile Clarias gariepinus . After a preliminary short-term (96 hours) static toxicity tests, fish were exposed to four sub-lethal concentrations (30, 45, 60 and 75 % of the LC 50 corresponding to 67, 101, 135 and 169 mg/l respectively) and a control group containing clean water using a semi-static renewal method for 90 days. Water quality parameters, heavy metals and total petroleum hydrocarbon (TPH) were determined using standard methods. After the exposure period, liver, brain and gill were harvested, labeled and prepared for photomicrography. Chloride, conductivity, salinity, magnesium, biochemical oxygen demand, chemical oxygen demand, total dissolve solids, turbidity and nitrate levels increased significantly (p 0.05). Values of TPH increased (p<0.05) with increasing concentrations of the crude oil. All analysed heavy metals followed a direct proportional trend as their values increased (p<0.05) alongside concentrations. Several histopathological alterations were found in the liver (sinusoidal congestion, atrophy of hepatocytes, hepatocellular degeneration and diffuse coagulation necrosis of hepatocytes), brain (vascular congestion and atrophy of neurons, neuronal necrosis, gliosis and loss of neurons) and gill (moderate loss of the secondary gill lamellae, moderate lamellae atrophy and moderate diffuse lamellae hyperplasia). The intensity of these lesions increased with increase in exposure dose. Keywords: Toxicity, Petroleum, Heavy metals, Water quality, Organs, Clarias gariepinus , LC 50

Acute toxicity and histopathological changes in livers of frog tadpoles (Hoplobatrachus rugulosus) exposed to bioinsecticides derived from Azadirachta indica A. Juss., Stemona curtisii Hook.F., and Mammea siamensis

Azadirachta indica A. Juss., Stemona curtisii Hook.F., and Mammea siamensis are popularly used as bioinsecticides by Thai farmers. To evaluate their safety on frog (Hoplobatrachus rugulosus) tadpoles, the ecologically and economically important species of Thailand, an acute static toxicity test was performed. The tadpoles (n = 10 per treatment group) were exposed to the bioinsecticides from A. indica (NSAI 5, 10, 15, 20, and 25 g/l) and the mixture of S. curtisii and M. siamensis (SCMS 0.8, 1.2, 1.6, 2.0, and 2.4 mg/l). It was found that the median lethal concentration (LC50) values at 96 h of the NSAI and the SCMS were 11.81 and 1.44 mg/l respectively. Hepatic failures were observed in tadpoles exposed to the NSAI and the SCMS. Histopathological changes included vacuolation, leukocyte infiltration, necrotic cell, and blood congestion. These lesions were more severe in the tadpoles treated with the NSAI or the SCMS at the high concentrations. Additionally, necrosis of bile duct epithelium, karyolysis, and sinusoidal dilation were apparently found in the tadpole exposed to 25 g/l of the NSAI, while the degeneration of bile duct was noted in the 1.6–2.4 mg/l of the SCMS-treated groups. However, the tadpoles exposed to 5 g/l of the NSAI showed only mild pathological changes in their livers. From a higher value of LC50 of the NSAI than the SCMS together with the mild histopathological changes in the tadpoles exposed to the low concentrations, thus the NSAI is less toxic to H. rugulosus tadpoles than the SCMS.

Effects of CFT Legumine (5% Rotenone) on Tadpole Survival and Metamorphosis of Chiricahua Leopard Frogs Lithobates chiricahuensis, Northern Leopard Frogs L. pipiens, and American Bullfrogs L. catesbeianus

AbstractAmphibians may experience collateral effects if exposed to CFT Legumine (5% rotenone), a piscicide that is used to remove invasive fish. A series of 48‐h static toxicity tests assessed the acute effects of CFT Legumine on multi‐aged tadpoles of the federally listed Chiricahua leopard frog Lithobates chiricahuensis, the widespread northern leopard frog L. pipiens, and the increasingly invasive American bullfrog L. catesbeianus. At the earliest Gosner stages (GS 21–25), Chiricahua leopard frogs were more sensitive to CFT Legumine (median lethal concentration [LC50] = 0.41–0.58 mg/L) than American bullfrogs (LC50 = 0.63–0.69 mg/L) and northern leopard frogs (LC50 = 0.91 and 1.17 mg/L). As tadpoles developed (i.e., increase in GS), their sensitivity to rotenone decreased. In a separate series of 48‐h static nonrenewal toxicity tests, tadpoles (GS 21–25 and GS 31–36) of all three species were exposed to piscicidal concentrations of CFT Legumine (0.5, 1.0, and 2.0 mg/L) to assess postexposure effects on metamorphosis. In survivors of all three species at both life stages, the time to tail resorption was nearly doubled in comparison with that of controls. For example, mid‐age (GS 31–36) Chiricahua leopard frog tadpoles required 210.7 h to complete tail resorption, whereas controls required 108.5 h. However, because tail resorption is a relatively short period in metamorphosis, the total duration of development (days from posthatch to complete metamorphosis) and the final weight did not differ in either age‐group surviving nominal concentrations of 0.5‐, 1.0‐, and 2.0‐mg/L CFT Legumine relative to controls. This research demonstrates that the CFT Legumine concentrations commonly used in field applications to remove unwanted fish could result in considerable mortality of the earliest stages of Lithobates species. In addition to acute lethality, piscicide treatments may result in delayed tail resorption, which places the tadpoles at risk by increasing their vulnerability to predation and pathogens.Received October 1, 2016; accepted January 17, 2017 Published online March 30, 2017

English

Abstract Invasive crayfish are known to displace native crayfish species, alter aquatic habitat and community structure and function, and are serious pests for fish hatcheries. White River Crawfish (WRC; Procambarus acutus) were inadvertently introduced to a warm-water fish hatchery in Missouri, USA, possibly in an incoming fish shipment. We evaluated the use of chemical control for crayfish to ensure incoming and outgoing fish shipments from hatcheries do not contain live crayfish. We conducted acute (≤ 24 hr) static toxicity tests to determine potency, dose-response, and selectivity of pesticides to WRC, Virile Crayfish (VC; Orconectes virilis), and Fathead Minnow (FHM; Pimephales promelas). Testing identified a formulation of cypermethrin (Cynoff®) as the most potent of five pesticides evaluated for toxicity to crayfish. A 4-hr exposure to a cypermethrin concentration of 100 μg·L-1 was found to kill 100% of juvenile and adult WRC; however, adult VC were not consistently killed. Concentrations of cypermethrin ≤ 100 μg·L-1 did not cause significant (&gt; 10%) mortality in juvenile FHM. Additional testing is needed to examine selectivity between crayfish and hatchery fish species. Biosecurity protocols at hatcheries that use chemical control have the potential to reliably prevent inadvertent transfers of live crayfish in fish shipments.

Effect of Methyl Parathion on Survival and Development of Tadpoles of Indian Cricket frog Fejervarya limnocharis

Amphibian populations are declining due to various causes including pesticide contamination in natural habitat. We evaluated effect of Methyl Parathion (MPT) an organophosphate pesticide on survival and development of common paddy field frog Fejervarya limnocharis in a laboratory condition. Effect of 0 µg MPT/L, 500 µg MPT/L, 1000 µg MPT/L, 1500 µg MPT/L, 2000 µg MPT/L and 3000 µg MPT/L was studied using static toxicity test for a duration of 28 days. MPT reduced the survival of tadpole. The mortality increased with the increased concentration of pesticide. The development decreased with increased MPT concentrations. At higher concentrations, MPT induced slow development and tadpoles failed to metamorphose. It is assumed that slow development could affect the larval life and amphibian population in agro-ecosystem.

Development of a groundwater fungal strain as a tool for toxicity assessment.

Despite the significant ecological role played by fungi in groundwater, their value as indicators of groundwater pollution is not known, as fungi are notoriously challenging to assess for toxicity because of their varied morphological components, in particular their filamentous structures. Hence they are rarely used in environmental risk assessments and monitoring programs for aquatic systems. A rapid, low cost, 1-step static toxicity test targeting the hyphal components of fungi was developed that subsequently demonstrated the sensitivity of a ubiquitous and dominant groundwater fungal strain to metal contaminants. The strain demonstrates sensitivity to chromium > copper > zinc and relative resistance to arsenic. The introduction of a novel group of groundwater microorganisms--the fungi-for toxicity evaluation will strengthen current risk assessment programs for these ecosystems.

Deconstructing the surrogate species concept: a life history approach to the protection of ecosystem services.

The use of the surrogate species concept is widespread in environmental risk assessment and in efforts to protect species that provide ecosystem services, yet there are no standard protocols for the choice of surrogates. Surrogates are often chosen on the basis of convenience or vague resemblances in physiology or life history to species of concern. Furthermore, our ability to predict how species of concern will fare when subjected to disturbances such as environmental contaminants or toxicants is often based on woefully misleading comparisons of static toxicity tests. Here we present an alternative approach that features a simple mathematical model parameterized with life history data applied to an assemblage of species that provide an important ecosystem service: a suite of parasitoid wasps that provide biological control of agricultural pests. Our results indicate that these parasitoid wasp species have different population responses to toxic insult--that is, we cannot predict how all four species will react to pesticide exposure simply by extrapolating from the response of any one species. Furthermore, sensitivity analysis of survivorship and reproduction demonstrates that the life stage most sensitive to pesticide disturbance varies among species. Taken together, our results suggest that the ability to predict the fate of a suite of species using the response of just one species (the surrogate species concept) is widely variable and potentially misleading.

Biochemical and genetic alterations in the freshwater neotropical fish Prochilodus lineatus after acute exposure to Microcystis aeruginosa

Microcystins are secondary metabolites produced by different species of cyanobacteria, such as Microcystis aeruginosa (MA). In this study, the biochemical and genetic effects of lyophilized MA were evaluated in the neotropical fish Prochilodus lineatus exposed to 1 or 2 mg L-1 lyophilized MA (treated group) or only water (control group) in static toxicity tests for 24 and 96 h. The gills and liver were used in the analysis of biotransformation enzymes and antioxidant defenses, blood and gill cells in genetic analysis and in brain and muscle it was determined the activity of acetylcholinesterase (AChE). The results showed the biotransformation pathway activation due to the increase in hepatic CYP1A and in branchial and hepatic glutathione S-transferase (GST). The antioxidant defense proved to be greatly affected by MA exposure leading to changes, both in gills and liver, in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and in the content of tripeptide glutathione (GSH). Lipid peroxidation was not detected, but damage to DNA molecule was observed in blood cells. In conclusion, it can be state the lyophilized MA is able to promote changes in the biochemical and genetic parameters of P. lineatus.

Metal speciation and toxicity of Tamar Estuary water to larvae of the Pacific oyster, Crassostrea gigas

As part of the PREDICT Tamar Workshop, the toxicity of estuarine waters in the Tamar Estuary (southwest England) was assessed by integration of metal speciation determination with bioassays. High temporal resolution metal speciation analysis was undertaken in situ by deployment of a Voltammetric In situ Profiling (VIP) system. The VIP detects Cd (cadmium), Pb (lead) and Cu (copper) species smaller than 4 nm in size and this fraction is termed ‘dynamic’ and considered biologically available. Cadmium was mainly present in the dynamic form and constituted between 56% and 100% of the total dissolved concentration, which was determined subsequently in the laboratory in filtered discrete samples. In contrast, the dynamic Pb and Cu fractions were less important, with a much larger proportion of these metals associated with organic ligands and/or colloids (45–90% Pb and 46–85% Cu), which probably reduced the toxicological impact of these elements in this system. Static toxicity tests, based on the response of Crassostrea gigas larva exposed to discrete water samples showed a high level of toxicity (up to 100% abnormal development) at two stations in the Tamar, particularly during periods of the tidal cycle when the influence of more pristine coastal water was at its lowest. Competitive ligand-exchange Cu titrations showed that natural organic ligands reduced the free cupric ion concentration to levels that were unlikely to have been the sole cause of the observed toxicity. Nonetheless, it is probable that the combined effect of the metals determined in this work contributed significantly to the bioassay response.

Effects of the organophosphate pesticide Folidol 600® on the freshwater fish, Nile Tilapia (Oreochromis niloticus)

Nile Tilapia (Oreochromis niloticus) juveniles were exposed to different concentrations of Folidol 600® in static toxicity tests. The 24, 48, 72 and 96h LC50 values of Folidol 600® to O. niloticus were 17.82, 8.91, 4.00 and 2.70mgL−1, respectively. The values of hematological parameters increased, and inhibition of cholinesterases activity (AChE, BChE and PChE) in plasma of fish exposed to the higher concentrations of pesticide reached 94%. Furthermore, the exposure of Tilapia to Folidol 600® caused an increase of 4%, 20% and 38.4% in oxygen consumption at 0.1, 0.5 and 1.0mgL−1, respectively. However, exposure to 2.5, 5.0 and 10mgL−1 caused a decrease of 33.6%, 35.2% and 42.4% in oxygen consumption relative to the control. The ammonium excretion of fish exposed to 0.0, 0.1, 0.5, 1.0, 2.5, 5.0 and 10.0mg Folidol 600®/L was 0.12, 0.18, 0.30, 0.33, 0.37, 0.36 and 0.33μg/g/min, i.e., 50%, 150%, 175%, 208%, 200% and 175% increase, respectively, relative to the control.

Comparison of amphipods Corophium insidiosum and C. orientale (Crustacea: Amphipoda) in sediment toxicity testing

The aim of this study was to compare the sensitivity of two Corophidae: Corophium orientale a standardized species and Corophium insidiosum a species more available in the Ionian sea (Southern Italy), in order to evaluate the suitability and applicability of C. insidiosum to sediment toxicity test. The sensitivity of the 2 species was compared through simultaneous bioassays: the 96-h static water-only toxicity test and a 10-day static sediment toxicity test. Sediment samples were collected in the Livorno harbour (Ligurian Sea). Both amphipods showed high sensitivity to reference toxicant and no significant differences were found between the two Corophiidae (t test; p > 0.05). Numerical Sediment Quality Guidelines (SQGs) have been used to relate the chemical concentrations of sediment samples to biological effects. Both amphipod species indicated the same sediment samples as potentially toxic according to chemical data. The results indicate that Corophium insidiosum would be suitable as an alternative test species to the recommended species C. orientale, in the development of sediment toxicity test.

Seasonal Variation in Sensitivity of Larval Sea Lampreys to the Lampricide 3‐Trifluoromethyl‐4‐Nitrophenol

AbstractWe evaluated the sensitivity of larval sea lampreys Petromyzon marinus to the lampricide 3‐trifluoromethyl‐4‐nitrophenol (TFM) in a series of toxicity tests in spring and summer. Although noted previously, the seasonal variation in sensitivity to TFM had never been tested as a means of reducing TFM usage in stream treatments. A preliminary study consisted of three spring and four summer static toxicity tests conducted at 12°C. A more comprehensive study consisted of 12 spring and summer paired flow‐through toxicity tests conducted both at seasonal water temperatures and at 12°C. The sensitivity of larval sea lampreys to TFM was greater in spring than in summer. The preliminary static toxicity tests indicated that the concentration of TFM needed to kill larval sea lampreys in spring (May and June) was about one‐half that required in summer (August); the concentrations lethal to 50% and 99.9% of the test animals (the LC50 and LC99.9 values) were less in spring than in summer. Analysis of variance of the flow‐through toxicity data indicated that season significantly affected both the LC50 and LC99.9 values. For all 12 paired flow‐through toxicity tests, the spring LC50 and LC99.9 values were less than the corresponding summer values. For 9 of the 12 paired flow‐through toxicity tests, the dose–response toxicity lines were parallel and allowed statistical comparison of the LC50 values. The spring LC50 values were significantly lower than the summer values in eight of the nine tests. Verification of a seasonal variation in the sensitivity of larval sea lampreys to TFM will allow inclusion of this factor in the selection model currently used by both the U.S. Fish and Wildlife Service and the Department of Fisheries and Oceans–Canada to schedule lampricide stream treatments.

Species Sensitivity to Copper

Channel catfish, Ictalurus punctatus (Rafinesque 1818), and sunshine bass, female white bass Morone chrysops (Rafinesque 1820) × male striped bass M. saxatilis (Walbaum 1792), juveniles (10 and 12 g, respectively) were exposed to copper sulfate (CuSO4) in a series of static toxicity tests to observe species sensitivity. The water used in this study was 18.9°C filtered well water with initial pH of 8.71, and total alkalinity and total hardness of 224 and 110 mg/L, respectively. Estimates of mean 96-hour median lethal concentration (LC50) values were 1.75 mg/L Cu (6.89 mg/L CuSO4) for channel catfish and 0.85 mg/ L Cu (3.35 mg/L CuSO4) for sunshine bass; LC50 values were calculated using nominal CuSO4 concentrations. These values differed significantly. This study demonstrates that sunshine bass juveniles are less tolerant of CuSO4 than channel catfish fingerlings when exposed concurrently in waters from the same source.

Evaluation of toxicity of capsaicin and zosteric acid and their potential application as antifoulants

The toxicity of two natural product antifoulants, capsaicin and zosteric acid, was evaluated using the Microtox assay and a static toxicity test. The EC50 values obtained from the Microtox assay for capsaicin and zosteric acid were 11.75 +/- 1.02 and 442 +/- 100 mg/L, respectively. The static toxicity test, conducted with freshwater organisms, yielded capsaicin EC50 values of 5.5 +/- 0.5 and 23 +/- 2.0 mg/L for P. putida and Lake Erie bacteria, respectively. Zosteric acid EC50 values were 167 +/- 3.9 and 375 +/- 10 mg/L for P. putida and Lake Erie bacteria, respectively. Tests with marine organisms resulted in capsaicin EC50 values of 6.9 +/- 0.2 and 15.6 +/- 0.4 mg/L for V. natriegens and V. parahaemolyticus, respectively; whereas zosteric acid EC50 values were 7.4 +/- 0.1 and 18 +/- 0.6 mg/L for V. natriegens and V. parahaemolyticus, respectively. These results indicate that zosteric acid is much less toxic than capsaicin and that both are substantially less toxic than the currently used antifoulants, such as TBT (EC50 < 0.01 ppb). Their effectiveness as natural antifoulants was demonstrated by preliminary attachments studies. As the aqueous antifoulant concentration increased, significant inhibition of bacteria attachment or prevention of biofilm formation was achieved. Hence, both capsaicin and zosteric acid could be attractive alternatives as new antifouling compounds.

EVALUASI TOKSISITAS INSEKTISIDA TERHADAP IKAN NILA (Oreochromis niloticus)

Evaluation of acute toxicity of endosulfan insecticide in natural water environment was conducted to know its potential negative effect to the Nile (Oreochromis nitoticusi. Using static toxicity test method, the acute toxicity of7 endosulfan concentration levels were tested afterstandardized for 96 hours in the solution of water from river, pond and paddy field. Four replications were implemented into those treatment and ground water was being a control. The size of Nile used in the examination was 3-5 gr/tails in weight. Result of the examination was revealed by medium lethal concentration value LC50 -96 hours. The result indicated that insecticide of endosulfan in the solution of water from three kind environment had the high toxicity effection the Nile. The values of LC50 -96 hours were 6.00 mg/Lin the river water, 4.61 mg/Lin the pond water and4.51 mg/Lin the paddy field water, respectively. The difference of those values was caused by the difference of water quality such as total hardess, organic matters, total and suspended solid, and endosulfan residue in the water.

Acute morphological and physiological effects of lead in the neotropical fish Prochilodus lineatus

The present study investigated lead effects on gill morphology, hematocrit, blood sodium, glucose, lipids, protein, and cholesterol of Prochilodus lineatus exposed to two sublethal lead concentrations for 96 h. Preliminary series of short-term static toxicity tests were run to determine LC50 (96 h) of lead in P. lineatus, which was 95 mg Pb.L-1. Therefore, lead concentrations tested in the sublethal experiments were 24 and 71 mg Pb.L-1, which correspond to 25% and 75% of the LC50 (96 h), respectively. Gills of P. lineatus exposed to both lead concentrations during 96 h presented a higher occurrence of histopathological lesions such as epithelial lifting, hyperplasia, and lamellar aneurism. P. lineatus did not show significant alterations in hematocrit during exposure to both lead concentrations. Fish exposed to the highest lead concentration showed a significant decrease in Na+ plasma concentration after 48 h, possibly reflecting a sodium influx rate decrease. P. lineatus exposed to both lead concentrations presented a "classical general adaptation syndrome to stress", as hyperglycemia associated with lowered lipids and proteins was reported. Stress-response magnitude was dose-dependent. While the response to the lowest lead concentration might represent adaptation, the highest concentration seems to characterize exhaustion.

Toxicity of chlorpyrifos adsorbed on humic colloids to larval walleye (Stizostedion vitreum).

After application, organophosphorus insecticides (OPs) are often strongly adsorbed to soil constituents. Because of their relatively low water solubility, OPs may be transferred from field to stream adsorbed on suspended solids. However, we are not aware of research done to evaluate the bioavailability (i.e., toxicity) of OPs transported on suspended solids to fish. We conducted 48-h static toxicity tests to determine the toxicity of chlorpyrifos in aqueous solution and adsorbed on calcium-saturated humic acid (HA) to three larval stages of walleye (Stizostedion vitreum). Three concentrations of chlorpyrifos adsorbed on HA, a HA control, and a chlorpyrifos-only treatment were tested. Fish that survived the 48-h static toxicity tests were analyzed to determine total cholinesterase (ChE) activity. In general, survival of all larval stages of walleye exposed to chlorpyrifos-HA complexes was less than that of walleye exposed to HA controls and the chlorpyrifos-only treatment, which were not toxic to walleye. Cholinesterase inhibition of larval walleye exposed to chlorpyrifos-HA complexes was similar to the ChE inhibition observed in larval walleye exposed to chlorpyrifos in the aqueous phase. These laboratory experiments indicate potential toxicity of chlorpyrifos-soil complexes to larval fish.