Piperonyl butoxide potentiates the synaptosome ATPase inhibiting effect of pyrethrin

Pyrethrins are widely used insecticides in both agriculture and households. In many commercial formulations piperonyl butoxide (PBO) is used with pyrethrins. PBO is a well-known synergist of pyrethrins, used to intensify their effects. One of the cellular targets of pyrethrins is the sodium channel in the membrane. In the present study, the activity of the membrane-bound integral protein ATPase was studied as a biomarker for the membrane effects of pyrethrin and PBO. Cerebral synaptosomes of rat brain were used in the study. The isolation of synaptosomes was performed with the Percoll gradient method. Both total ATPase and Mg2+ activated ATPase were studied by determining inorganic phosphate. Exposure to 0.1-1000 microM of pyrethrin and to 0.4-4000 microM of PBO decreased ATPase activity dose-dependently. The most efficient mixture was the one consisting of one part of pyrethrin and four parts of PBO. The activity of total ATPase decreased 15% in concentrations of 0.1-10 microM pyrethrin, and a 50% decrease was found at 100 microM pyrethrin. The mixture of pyrethrin and PBO caused a 15-60% decrease in the total ATPase activity at 0.1-10 microM pyrethrin and 0.4-40 microM PBO. A 85% decrease was found after exposure to the mixture of 100 microM pyrethrin and 400 microM PBO. PBO alone had no effect at 0.4-40 microM concentrations, but a marked effect was seen at over 40 microM concentrations. The results indicate that PBO is an effective synergist of pyrethrin and that it is very toxic in high concentrations. The results also confirm that neuronal sodium homeostasis is one target of the neurotoxic effect of pyrethroid compounds.     

Effects of synthetic pyrethroids and methidation on activities of some digestive enzymes in carp (Cyprinus carpio L.).

The effects of pyrethroid pesticides (deltamethrin, permethrin and cypermethrin) and an organophosphate ester (methidation) on the activities of carp trypsin, alpha-chymotrypsin, carboxypeptidase A and lipase were studied. The enzymes were isolated from the gastrointestinal tract and the effects of the pesticides were investigated during incubation for 5 min. The activity of trypsin was influenced only slightly by the presence of deltamethrin and methidation, whereas permethrin and cypermethrin caused significant inhibition. The pyrethroid pesticides at lower concentrations resulted in a slight activation of alpha-chymotrypsin. Methidation inhibited the alpha-chymotrypsin activity by about 20%. These pesticides modified the lipase activity to a lesser extent; the highest inhibition was measured with cypermethrin. The carboxypeptidase A activity was inhibited by both pyrethroid pesticides and methidation. The results suggest that these pesticides might interact with the active conformation of the studied hydrolytic enzymes, resulting in changes in their activities.     

Effects of synthetic pyrethroids and methidation on activities of some digestive enzymes in carp (Cyprinus carpio L.)

Abstract

The effects of pyrethroid pesticides (deltamethrin, permethrin and cypermethrin) and an organophosphate ester (methidation) on the activities of carp trypsin, α‐chymotrypsin, carboxypeptidase A and lipase were studied. The enzymes were isolated from the gastrointestinal tract and the effects of the pesticides were investigated during incubation for 5 min. The activity of trypsin was influenced only slightly by the presence of deltamethrin and methidation, whereas permethrin and cypermethrin caused significant inhibition. The pyrethroid pesticides at lower concentrations resulted in a slight activation of α‐chymotrypsin. Methidation inhibited the α‐chymotrypsin activity by about 20%. These pesticides modified the lipase activity to a lesser extent; the highest inhibition was measured with cypermethrin. The carboxypeptidase A activity was inhibited by both pyrethroid pesticides and methidation. The results suggest that these pesticides might interact with the active conformation of the studied hydrolytic enzymes, resulting in changes in their activities.     

Comparative study on the environmental risk induced by several pyrethroids in estuarine and freshwater invertebrate organisms

The acute toxicity of permethrin, resmethrin, and cypermethrin to four species of aquatic non-target invertebrate organisms, found in estuarine and freshwater ecosystems, was evaluated. Artemia franciscana and Brachionus plicatilis larvae, as estuarine organisms, and Brachionus calyciflorus and Thamnocephalus platyurus larvae, as freshwater organisms, were exposed for 24 h to concentrations of these pyrethroids, and the LC(50) values were compared. The freshwater organisms were more sensitive to these pyrethroids than estuarine organisms tested. A. franciscana larvae were more tolerant organisms than B. plicatilis larvae. The freshwater organisms tested have demonstrated to be a good alternative to the standard acute toxicity assays using Daphnia, although Brachionus plycatilis larvae were more sensitive to these pyrethroid insecticides than T. platyurus. Analysis of 24 h LC(50) values of these pyrethroids, determined by static bioassays, revealed that the rank order of toxicity was: permethrin相似文献   

Antiandrogenic activity of pyrethroid pesticides and their metabolite in reporter gene assay

Many pesticides possess hormonal activity and have thus been classified as endocrine disruptors. Pyrethroids are commonly used pesticides worldwide, but little has been done to characterize their antiandrogenic activity potential. We tested three frequently encountered pyrethroids (fenvalerate, cypermethrin, permethrin) and their metabolite 3-phenoxybenzoic acid (3-PBA) for antiandrogenic and androgenic activity using a human androgen receptor (AR) mediated luciferase reporter gene assay in CV-1 African green monkey kidney cell. The assay displayed appropriate response to the known AR agonist 5alpha-dihydrotestosterone and AR antagonist nilutamide and flutamide. At 0.1mM, all the three tested pyrethroids significantly suppressed the luciferase expression. Further, their metabolite 3-PBA also showed antagonist activity. None of the test chemicals showed androgenic activity. Through the antiandrogenic pathways, exposure to certain pyrethroids may contribute to the damage of reproductive system. In conclusion, pyrethroid pesticides can act as antiandrogen in vitro, and metabolizing to 3-PBA cannot eliminate the antagonist activity. This result provides useful information for risk assessment of pyrethroid pesticides.     

A field study on residues of four insecticides used in strawberry protection

Abstract

In 1986 strawberry plots were treated with dimethoate, malathion, permethrin and cypermethrin at 80% bloom of primary flowers. In 1987 the plots were sprayed with dimethoate, malathion and permethrin at 30% bloom. Residue analysis of these insecticides on the flowers were analyzed using solvent extraction and gas liquid chromatography. Residue analysis at 0 to 18 days on flowers and fruit showed an exponential decrease. Organophosphates tended to degrade more quickly than synthetic pyrethroids. The results are discussed in the context of an integrated pest management program.     

Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria endemic area in South Africa

DDT and pyrethroids were determined in 152 breast-milk samples from three towns in KwaZulu-Natal, South Africa, one of which had no need for DDT for malaria control. All compounds were found present in breast milk. Primiparae from one town had the highest mean SigmaDDT whole milk levels (238.23 microg/l), and multiparae from the same town had the highest means for permethrin (14.51 microg/l), cyfluthrin (41.74 microg/l), cypermethrin (4.24 microg/l), deltamethrin (8.39 microg/l), and Sigmapyrethroid (31.5 microg/l), most likely derived from agriculture. The ADI for DDT was only exceeded by infants from one town, but the ADI for pyrethroids was not exceeded. Since the ADI for DDT was recently reduced from 20 to 10 microg/kg/bw, we suggest that this aspect be treated with concern. We therefore raise a concern based on toxicant interactions, due to the presence of four different pyrethroids and DDT. Breastfeeding however, remains safe under prevailing conditions.     

The synthetic pyrethroid isomers II. Biological activity

Abstract

Pure optical isomers of phenothrin, permethin and cypermethrin were synthesised and tested on a wide spectrum of insects (Blattella germanica, Leptinotarsa decemlineata, Tribolium confusum, Oncopeltus fasciatus, Musca domestica, Aedes aegypti). Our results suggest that in the structurally related series phenothrin, permethrin and cypermethrin the chemical modifications had only a small influence on intrinsic activity of the compounds at the target site. The activity of piperonylbutoxide synergised 1Rtrans phenothrin and 1Rcis permethrin (LD₅₀=1.2 ng/fly in both cases) is in a similar range to the most active 1RcisS cypermethrin isomer alone or with PB (LD₅₀=0.9 and 0.4 ng/fly, respectively). Some cypermethrin isomers considered previously to be totally inactive show significant activity depending on the tested insect species. The 1ReisR and 1RtransR isomers proved to be as active as the most potent isomers on mosquito. A similarly unexpected result was that in the case of mosquito all four trans isomers were significantly more active than the corresponding eis isomers.

The superiority of the (S)‐α configuration over (R)‐α was found. It does not result from a higher intrinsic activity at the target site, but rather from the enhanced metabolic resistance of (S)‐α‐esters to ester cleavage as confirmed by Synergist studies. The activity of the two most potent stereoisomers, 1ReisS and 1RtransS, could not be elevated by quinalphos, while the inactive 1ScisR and 1StransR isomers showed significant activity with the esterase inhibitor quinalphos administered sublethally.

In contrast with the antagonism between (S)‐ and (R)‐α‐epimers of cypermethrin reported earlier a considerable synergism was observed between 1RtransS and 1StransR enantiomer pair on flour beetle and housefly in tarsal contact tests.

The results with stereoisomers and their mixtures were utilised in the development of two new products, Chinmix (beta‐cypermetrhin) and Transmix (theta‐cypermetrhin).     

Anthropogenic and naturally-produced organobrominated compounds in bluefin tuna from the Mediterranean Sea

In the present study, bioaccumulation potential of two pyrethroid insecticides, bifenthrin and permethrin, was measured using a Lumbriculus variegatus sediment bioaccumulation test. Two sediments differing in their physical characteristics and two different aging periods were tested. Desorption rates measured by Tenax extraction suggested that pyrethroids were bioavailable to L. variegatus, however bioavailability varied among chemicals, sediments and aging time, and was greater for permethrin than bifenthrin. The relatively low biota-sediment accumulation factor (BSAF) values resulted from the extensive biotransformation of pyrethroids by L. variegatus. Biotransformation capacity of L. variegatus to permethrin was further studied with a water-only exposure, and the percentage parent compound dropped to 36.0% after 14 d. These results indicated sediment-associated pyrethroids were bioavailable to L. variegatus, however bioaccumulation was limited because L. variegatus was capable of biotransforming the pyrethroids.     

Changes in hematological and serum biochemical values in jundiá Rhamdia quelen due to sub-lethal toxicity of cypermethrin

Jundiá (Rhamdia quelen, Quoy and Gaimard), a South American teleostean fish, was exposed to sub-lethal concentrations of cypermethrin (30% and 45% of the 48-h LC(50) value of 0.265 ppm) for 2, 4 or 8 days. Serum biochemical and hematological values and behavioral changes were studied. The 30% LC(50), 0.08 ppm, produced significant increases in Mg(2+), P, K(+), creatinine, urea, glucose, cholesterol, aspartate aminotransferase and alkaline phosphatase levels, and reduction in total proteins and triglycerides in serum. The 45% LC(50), 0.12 ppm, produced significant increase in Na(+), Mg(2+), P, K(+), creatinine, urea, glucose, cholesterol, and alkaline phosphatase, and reduction in triglycerides and alanine aminotransferase levels in serum. At this concentration, the fish showed behavior changes such as hyper-excitability, asphyxia, and widening of mouth and operculum. The hematological values remained normal, except for hemoglobin concentrations and the mean corpuscular hemoglobin concentration, which increased with exposure to 0.08 ppm and 0.12 ppm cypermethrin. Results of the present work show that biochemical analysis of serum can be useful to detect incipient cypermethrin intoxication of the shoal.     

Biomarkers assessment in juvenile Cyprinus carpio exposed to waterborne cadmium

The impact of long-term exposure to waterborne cadmium (Cd) on Cyprinus carpio was evaluated through changes of selected parameters considered as biomarkers of toxicity. Fish were exposed to 1.6 mg l(-1) Cd for 14 days and then transferred to Cd-free water for 19 days. The measured parameters were gill ATPases, brain acetylcholinesterase (AchE), liver glutamate oxaloacetate (GOT) and glutamate pyruvate (GPT) transaminases, muscle water content, and protein content of liver, gills and brain. Condition factor and liver somatic index were also calculated. Branchial ATPase activities were impaired in a dissimilar way: the (Na(+),K(+))-ATPases were inhibited by approximately 30%, while the Mg(2+)-ATPase was significantly activated by 70%. Brain AchE showed no changes after Cd exposure. Both liver GOT and GPT activities were increased by the metal by 63 and 98%. Water content of the skeletal muscle showed no significant alterations. After the 19-day recovery phase, changes in the Mg(2+)-ATPase and GPT were reversed to values similar to controls, but the Cd exposure resulted in an irreversible alteration in GOT activity. Results indicate that the sublethal Cd concentrations are stressful to carp, particularly with reference to branchial enzymes which may disrupt the osmotic and ionic balance of the animals.     

Occurrence,compositional distribution,and toxicity assessment of pyrethroid insecticides in sediments from the fluvial systems of Chaohu Lake,Eastern China

Surface sediment-associated synthetic pyrethroid insecticides (SPs) are known to pose high risks to the benthic organisms in Chaohu Lake, a shallow lake of Eastern China. However, the pollution status of the lake’s tributaries and estuaries is still unknown. The present study was conducted to investigate the occurrence, compositional distribution, and toxicity of 12 currently used SPs in the surface sediments from four important tributaries, as well as in the sediment cores at their estuaries, using GC-MS for quantification. All SPs selected were detectable, with cypermethrin, es/fenvalerate, and permethrin dominant in both surface and core sediments, suggesting that these compounds were extensively applied. Urban samples contained the highest summed concentrations of the 12 SPs analyzed (Σ₁₂SP) in both surface and core sediments compared with rural samples, suggesting that urban areas near aquatic environments posed high risks for SPs. The mean concentration of Σ₁₂SP in surface sediments of each river was generally higher than that found in core sediments from its corresponding estuary, perhaps implying recent increases in SP usage. Surface sediments were significantly dominated by cypermethrin and permethrin, whereas core sediments were dominated by permethrin and es/fenvalerate. The compositional distributions demonstrated a spatial variation for surface sediments because urban sediments generally contained greater percentages of permethrin and cypermethrin, but rural sediments had significant levels of es/fenvalerate and cypermethrin. In all sediment cores, the percentage of permethrin gradually increased, whereas es/fenvalerate tended to decrease, from the bottom sediments to the top, indicating that the former represented fresh input, whereas the latter represented historical residue. Most urban samples would be expected to be highly toxic to benthic organisms due to the residue of SPs based on a calculation of toxic units (TUs) using toxicity data of the amphipod Hyalella azteca. However, low TU values were found for the samples from rural areas. These results indicate that the bottom sediments were exposed to high risk largely by the residual SPs from urban areas. The summed TUs were mostly attributable to cypermethrin, followed by λ-cyhalothrin and es/fenvalerate. Despite permethrin contributing ～28.7 % of the Σ₁₂SP concentration, it only represented 6.34 % of the summed TUs. Therefore, our results suggest that high levels of urbanization can increase the accumulation of SPs in aquatic environments.     

Oxidative stress in Scenedesmus sp. during short- and long-term exposure to Cu2+ and Zn2+

Algae are exposed to elevated levels of heavy metals in water bodies generally for a long-term, and occasionally for a short-term duration. The present study deals with oxidative stress in Scenedesmus sp., commonly found in nutrient-rich freshwaters, during short- (6h) and long-term (7d) exposure to Cu(2+) and Zn(2+). The cells accumulated almost 2- and 4-times more Cu(2+) and Zn(2+) inside the cells during long-term than during short-term exposure to these metals. But the data on photosynthetic O(2) evolution and cell viability suggest that Scenedesmus sp. experienced lesser metal stress in long-term than in short-term experiment. Although malondialdehyde content was slightly higher in the long-term experiment, the amount produced by one unit intracellular metal was significantly lower than that in the short-term experiment. Superoxide dismutase activity of Scenedesmus sp. was >30% higher during long-term than during short-term exposure to Cu(2+) and Zn(2+). But, catalase and ascorbate peroxidase activities increased only at 2.5 microM Cu(2+) and 25 microM Zn(2+) when oxidative stress was mild, but were inhibited at 10 microM Cu(2+) under intense oxidative stress. Cu(2+) and Zn(2+) reduced glutathione reductase activity and total SH content of Scenedesmus sp. in both the experiments, with greater reduction occurring in the long-term experiment. The depletion of total thiol was positively related with the intracellular level of metals. Thiols might have helped Scenedesmus sp. in overcoming metal-induced oxidative stress, but depletion of thiol pool is known to make cells vulnerable to oxidative stress. The study suggests that antioxidant enzymes play a role only under mild oxidative stress. An increased accumulation of proline seems to be an important strategy for alleviating metal-induced oxidative stress in Scenedesmus sp. The study shows that Scenedesmus sp. could acclimatize during long-term exposure to toxic concentrations of the test metals.     

Sublethal effect of silver and chromium in the green mussel Perna viridis with reference to alterations in oxygen uptake, filtration rate and membrane bound ATPase system as biomarkers

Perna viridis is an ideal animal for studying the impairment caused by the effects of heavy metals that are often detected in coastal areas. Preliminary bioassay tests revealed that the lethal (LC(100)), median lethal (LC(50)) and sublethal (LC(0)) concentration of silver and chromium to P. viridis were 6.5, 4.0, 2.0 mg l(-1) and 4.5, 2.5, 1.0 mg l(-1), respectively. Toxic effect of silver and chromium was evaluated in the green mussel P. viridis, with reference to oxygen consumption, filtration rate and ATPase system in laboratory experiments. These parameters were selected as the end point of sublethal stress. Oxygen consumption and filtration rates were calculated as a measure of decline in the dissolved oxygen level and algal concentration (feed) in the aquaria water, respectively. Silver and chromium affects both oxygen consumption and filtration rate significantly (P<0.01) at 96 h when compared to control. The activity of ATPases system in the gills, hepatopancreas, ovary and muscle of mussels were inhibited by silver and chromium indicating that metals exerted significant toxic effect. The inhibition of Na(+)K(+) ATPase, Ca(2+) ATPase and Mg(2+) ATPase in the mussels were significant (P<0.05) for silver and highly significant (P<0.01) for chromium, which indicates that chromium was more toxic to mussels when compared to silver. The assessment of oxygen consumption, filtration and ATPases system can thus be used as a valid biomarker in aquatic ecotoxicology studies.     

Occurrence and distribution of sediment-associated insecticides in urban waterways in the Pearl River Delta, China

Sediment-associated pesticides, including organochlorine (OCP), organophosphate (OP), and pyrethroid insecticides, were analyzed in urban waterways in three cities (Guangzhou, Dongguan, and Shenzhen) in the Pearl River Delta (PRD), China. The OCPs represented 27.2% of the detectable insecticides in sediment, and chlordanes, DDTs, and endosulfans were the most frequently detected OCPs. The currently used insecticide chlorpyrifos was the only OP detected above the reporting limit (RL), with concentrations ranging from <RL to 100 ng g⁻¹ dry weight (dw). Additionally, pyrethroids were detected in all sediments with the sum pyrethroid concentrations ranging from 4.26 to 384 ng g⁻¹ dw and this represented 64.9% of the sum insecticide concentration. Despite their widespread use, no studies have been conducted investigating the occurrence and distribution of pyrethroids in China. As the first report of pyrethroids in urban waterways in China, the current study found cypermethrin was the most abundant insecticide detected in the PRD at concentrations ranging from 1.44 to 219 ng g⁻¹ dw. Spatially, sediment from more populous and urbanized areas (Shenzhen and Tianhe district in Guangzhou) had higher insecticide residues than less populous agricultural areas. In the more modernized city of Shenzhen, the OCPs were seldom detected, whereas more diverse patterns of pyrethroids were observed. Potential sources of these insecticides, especially the frequently detected pyrethroids, were most likely from pest control during urban landscaping maintenance and from abatement programs targeting mosquitoes and ants. Results suggested that a shift in application pattern and elevated urbanization increased accumulation of currently used insecticides like pyrethroids in sediment, and made them the predominate insecticides in the PRD urban waterways.     

Effect of anions and cations on cadmium sorption kinetics from aqueous solutions by chitin: experimental studies and modeling

The effect of ions, including Na(+), Mg(2+), Ca(2+), Cl(-), SO(4)(2-) and CO(3)(2-), at various initial concentrations, on the kinetics of cadmium sorption by chitin was studied at 25 degrees C and free initial pH solution in batch conditions. The presence of these ions in solution was found to inhibit the uptake of cadmium by chitin to different degrees: sodium and chloride ions have no significant effect. For Mg(2+), Ca(2+), SO(4)(2-) and CO(3)(2-) ions, the effects ranged from a large inhibition of cadmium by Ca(2+) and CO(3)(2-) to a weak inhibition by Mg(2+) and SO(4)(2-). These results indicate that the uptake sites of these ions are the same. No ion was found to enhance cadmium uptake. The results also showed that the kinetics of sorption are best described by a pseudo second-order expression than a first or second-order model.     

Sub-chronic effect of neem based pesticide (Vepacide) on acetylcholinesterase and ATPases in rat.

Acetylcholinesterases (AChE), Na(+)-K+, Mg2+ and Ca(2+)-ATPases were monitored in rat brain when treated orally with 80, 160 and 320 mg/kg of Vepacide, an active ingredient from neem seed oil, daily for 90 days. Brain AChE, Na(+)-K+ and Ca(2+)-ATPases were inhibited whereas Mg(2+)-ATPase levels were enhanced in both the sexes after 45 and 90 days of treatment. The relative sensitivities of these ATPases to Vepacide indicated that Ca(2+)-ATPase being more sensitive than Na(+)-K(+)-ATPase in both the sexes. The magnitude of Ca(2+)-ATPase inhibited by this compound was higher than that of brain AChE. It appears to be sexual dimorphism in the alterations of brain AChE, Na(+)-K+ and Mg(2+)-ATPases by Vepacide with females being significant when compared with males. After 28 days of post treatment the alterations observed were approached to those of controls both in male and female rats showing reversal of the toxicity. These results indicated that the ATPases were potently inhibited by Vepacide and seemed to be its precise target among the enzyme studied. This can be used as biochemical marker of exposure to this neem derived product.     

Toxic effects of low concentrations of Cu on nodulation of cowpea (Vigna unguiculata)

Although Cu is phytotoxic at Cu(2+) activities as low as 1-2 microM, the effect of Cu(2+) on the nodulation of legumes has received little attention. The effect of Cu(2+) on nodulation of cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) was examined in a dilute solution culture system utilising a cation exchange resin to buffer solution Cu(2+). The nodulation process was more sensitive to increasing Cu(2+) activities than both shoot and root growth; whilst a Cu(2+) activity of 1.0 microM corresponded to a 10% reduction in the relative yield of the shoots and roots, a Cu(2+) activity of 0.2 microM corresponded to a 10% reduction in nodulation. This reduction in nodulation with increasing Cu(2+) activity was associated with an inhibition of root hair formation in treatments containing > or =0.77 microM Cu(2+), rather than to a reduction in the size of the Rhizobium population.     

Effects of the synthetic pyrethroid insecticide, permethrin, on two estuarine fish species

Limited toxicity data are available for estuarine and marine species and the widely used pyrethroid insecticide, permethrin. This study determined acute effects of permethrin on survival, lipid peroxidation, acetylcholinesterase activity, and splenocyte proliferation for two fish species found in South Carolina estuaries; juvenile red drum (Sciaenops ocellatus) and adult mummichog (Fundulus heteroclitus). Juvenile S. ocellatus were significantly more sensitive than adult F. heteroclitus to permethrin exposure, with a 96-h LC50 value of 8 μg/L determined for red drum compared to 23 μg/L for mummichog. Lipid peroxidation activity of the liver increased in permethrin-treated fish compared to control animals after 24 h and decreased after 96 h. Permethrin had no effect on acetylcholinesterase activity of the brain at the concentrations tested. Permethrin exposure significantly inhibited splenocyte proliferation, indicating an immunosuppressive effect. Most of the effects of permethrin on fish cellular stress enzymes and survival occurred at concentrations much higher than those typically measured in the environment. However, inhibition of splenocyte proliferation in juvenile red drum occurred at approximately twice that of measured permethrin concentrations in surface water. These findings may prove useful to the future management and regulation of pyrethroid insecticide use near estuarine habitats.     

The response of Chenopodium album L. and Abutilon theophrasti Medik. to reduced doses of mesotrione

Limited toxicity data are available for estuarine and marine species and the widely used pyrethroid insecticide, permethrin. This study determined acute effects of permethrin on survival, lipid peroxidation, acetylcholinesterase activity, and splenocyte proliferation for two fish species found in South Carolina estuaries; juvenile red drum (Sciaenops ocellatus) and adult mummichog (Fundulus heteroclitus). Juvenile S. ocellatus were significantly more sensitive than adult F. heteroclitus to permethrin exposure, with a 96-h LC50 value of 8 μg/L determined for red drum compared to 23 μg/L for mummichog. Lipid peroxidation activity of the liver increased in permethrin-treated fish compared to control animals after 24 h and decreased after 96 h. Permethrin had no effect on acetylcholinesterase activity of the brain at the concentrations tested. Permethrin exposure significantly inhibited splenocyte proliferation, indicating an immunosuppressive effect. Most of the effects of permethrin on fish cellular stress enzymes and survival occurred at concentrations much higher than those typically measured in the environment. However, inhibition of splenocyte proliferation in juvenile red drum occurred at approximately twice that of measured permethrin concentrations in surface water. These findings may prove useful to the future management and regulation of pyrethroid insecticide use near estuarine habitats.