Relationship closeness of tolerance to two neonicotinoids with their internal body burden in two estuarine resident marine crustaceans.

The estuarine resident crustacean sand shrimp, Crangon uritai, has a higher tolerance to neonicotinoid insecticides than that of the kuruma prawns, Penaeus japonicus. However, the reason for the differential sensitivities between the two marine crustaceans remains to be understood. This study explored the mechanism underlying differential sensitivities based on insecticide body residues after exposing both said crustaceans to two insecticides (acetamiprid and clothianidin) with or without oxygenase inhibitor piperonyl butoxide (PBO) for 96 h. Two graded-concentration groups were formed; group H (1/15-1 times the 96-h LC50 values) and L (one-tenth the concentration of group H). Results showed that the internal concentration in survived specimens tended to be lower in sand shrimp than in kuruma prawns. Co-treatment of PBO with two neonicotinoids not only increased sand shrimp mortality in the H group, but also altered metabolism of acetamiprid into its metabolite, N-desmethyl acetamiprid. Furthermore, molting during the exposure period enhanced bioconcentration of insecticides, but not affects survival. Collectively, the higher tolerance of sand shrimp than that of kuruma prawns to the two neonicotinoids can be explained by lower bioconcentration potential and more involvement of oxygenase in their alleviating lethal toxicity.

Tracing and regulating redox homeostasis of model benthic ecosystems for sustainable aquaculture in coastal environments.

Aquaculture in coastal environments has an increasingly important role in the world's food supply; however, the accumulation of organic compounds on seafloors due to overfeeding adversely affects benthic ecosystems. To assess the ecological resilience of aquafarms to nutrient influx, we investigated the redox homeostasis of benthic ecosystems using a marine oligochaete as a model benthic organism in aquaculture fields. Real-time monitoring of the redox potential of a model benthic ecosystem constructed in an electrochemical reactor allowed evaluation of the homeostatic response of the system to nutrient addition. Although the detrimental effects of overfeeding were confirmed by irreversible potential changes in the sediment, redox homeostasis was reinforced through a cooperative relationship between oligochaetes and sediment microorganisms. Specifically, the oligochaetes exhibited reversible changes in metabolism and body position in response to dynamic changes in the sediment potential between -300 and 500 mV, thereby promoting the decomposition of organic compounds. The potential-dependent changes in metabolism and body position were reproduced by artificially manipulating the sediment potential in electrochemical reactors. Given the importance of benthic animals in sustaining coastal ecosystems, the electrochemical monitoring and physiologic regulation of marine oligochaetes could offer an intriguing approach toward sustainable aquaculture.

Molting enhances internal concentrations of fipronil and thereby decreases survival of two estuarine resident marine crustaceans.

In aquatic arthropods, molting is a pivotal physiological process for normal development, but it may also expose them to higher risks from xenobiotics, because the organism may take up additional water during that time. This study aimed to assess the effects of molting on bioconcentration and survival after 96-h exposure to insecticide fipronil with or without oxygenase (CYP450s) inhibitor piperonyl butoxide (PBO) of two estuarine resident marine crustacean species: the sand shrimp Crangon uritai and the kuruma prawn Penaeus japonicus, with 96-h LC50 value of fipronil = 2.0 µg/L and 0.2 µg/L, respectively. Two graded concentrations included group high (H) (equivalent to the 96-h LC50 values) and low (L) (one-tenth of the H group concentration). Molting and survival were individually checked, and internal concentrations of fipronil and its metabolites (fipronil desulfinyl, fipronil sulfide, fipronil sulfone) were measured. The results showed that, only fipronil and fipronil sulfone were detected from organism, and that internal concentrations of these insecticides in molted specimens were higher than those of unmolted ones but comparable with those of dead ones. Accordingly, mortality was more frequent in molted specimens than those that were unmolted. Furthermore, involvement of oxygenase and higher lethal body burden threshold may confer higher tolerance to fipronil in sand shrimp than in the kuruma prawn. This study is the first to demonstrate that the body-residue-based approach is useful for deciphering the causal factors underlying fipronil toxicity, but highlights the need to consider physiological factors in arthropods, which influence and lie beyond body burden, molting and drug metabolism.

Integrated transcriptomic and metabolomic analyses reveal mechanism underlying higher resistance of the marine oligochaete Thalassodrilides cf. briani (Clitellata: Naididae) to heavy contamination of sediments with polycyclic aromatic hydrocarbons.

In some coastal areas, sediments are contaminated with various chemical compounds, causing significant threats to marine organisms. Therefore, the development of remediation techniques is important. Here, we focused on bioremediation using marine benthic animals such as aquatic oligochaetes. The oligochaete Thalassodrilides cf. briani is highly resistant to contamination of sediments with toxic chemicals. We examined whether T. cf. briani could decompose high-concentration polycyclic aromatic hydrocarbons (PAHs) in sediments. Furthermore, relevant genes expressed in T. cf. briani exposed to contaminated sediment were comprehensively examined using next-generation sequencing, and its metabolites were identified by metabolomic analysis using gas chromatography-mass spectrometry. T. cf. briani reduced the concentration of 16 PAHs in the sediment from 55,900 to 45,200 ng/g dry weight in 50 days, thereby reducing total PAH concentrations by approximately 20%. The results of transcriptomic analysis suggest that activation of a drug-metabolizing enzyme system may promote the metabolism of harmful chemical substances during excretion of chemicals from the body. According to the results of principal component analysis based on the values of 43 types of metabolomes identified by metabolomic analysis, groups were divided according to the difference in the number of exposure days. In addition, levels of glutamine, which is important for maintaining digestive tract functions, increased. This suggests that the digestive tract function promotes the metabolism and detoxification of foreign substances. Furthermore, transcriptome analysis revealed that glutamate dehydrogenase increased 1.3-fold and glutamine synthetase increased 1.7-fold, confirming the increase in glutamine. Thus, we conclude that T. cf. briani adapted to the polluted sediment by regulating its metabolism.

Immune toxicity of phenanthrene and its combined effects of white spot syndrome virus on the survival of kuruma shrimp (Penaeus Japonicus).

Shrimp inhabiting coasts that are frequented by humans are exposed to various pollutants. Additionally, viral infections that cause serious damage to shrimp populations have been observed in these environments. The present study sought to evaluate the immunotoxic effects of phenanthrene (Phe), a pollutant detected in coastal environments, on kuruma shrimp (Penaeus japonicus). We further examined the survival of shrimp following combined exposure to Phe (30 or 300 µg/L) and white spot syndrome virus (WSSV). Results show that exposure to Phe for seven days decreased immune system-related parameters, including total hemocyte count and phenoloxidase activity in hemolymph (p < 0.05). However, these effects were not detected after three days of exposure. Moreover, a combined exposure assay revealed that shrimp mortality increased following exposure to 300 µg/L Phe and infection with WSSV. The number of WSSV gene copies was also observed to increase in these co-exposed shrimp. Taken together, these results indicate that long-term Phe exposure impairs the immune system of P. japonicus, resulting in fatal proliferation of WSSV. Hence, considering that combined exposure to Phe and WSSV leads to increased mortality of shrimp, it is imperative that the detrimental effects elicited by multiple stresses be considered, and controlled, in areas inhabited by kuruma shrimp.

Alterations of stool metabolome, phenome, and microbiome of the marine fish, red sea bream, Pagrus major, following exposure to phenanthrene: A non-invasive approach for exposure assessment.

The present study aimed to assess the impact of phenanthrene (Phe) on fish health by addressing the alteration of fecal characteristics, in lieu of collecting biomarkers that often involves injurious or even fatal sampling of organisms. The marine fish red sea bream, Pagrus major, was exposed to Phe at a concentration of 18 µg/L for 16 days followed by depuration for 13 days. We collected feces from Phe-exposed or control (Phe-free) fish and then analyzed the fecal metabolite profile (metabolome), carbon utilization of microbiota (phenome), and bacterial 16s rRNA gene sequence (microbiome). Along with the increase in physiological stress markers (SOD and EROD) in serum and liver, we noted the possible role of intestine as a Phe reservoir. Furthermore, abnormal fecal appearance (green coloration) and remarkable changes in fecal characteristics were observed. These changes include alterations of cholesterol and putrescine metabolism and the enhanced utilization of putrescine as a carbon source. Phe also altered the microbial community, with an increase in Phe-degrading bacteria such as Pseudomonas. Interestingly, these enteric impairments were ameliorated by depuration. Taken together, our findings suggest that these alterations in feces were associated with adaptive responses to environmentally relevant Phe exposure scenarios, and that stool samples are potential candidates for exposure assessment in fish.

Ecological risk assessment of an antifouling biocide triphenyl (octadecylamine) boron in the Seto Inland Sea, Japan.

In this study, we derived the predicted no-effect concentrations (PNEC) for triphenyl (octadecylamine) boron (TPB-18) and investigated the occurrence of triphenylboranes (TPBs), including TPB-18, for ecological risk assessment in the Seto Inland Sea, Japan. We tested algal growth inhibition, crustacean immobilization, and reproductive toxicity and performed toxicity tests in fish to assess acute and chronic toxicity and generate the PNEC for TPB-18. The minimum toxicity value was 0.30 µg/L, as determined by the 72-h no-observed-effect concentration (NOEC) for the alga Chaetoceros gracilis. The 5th-percentile of hazardous concentration (HC5), derived from NOECs using the species sensitivity distributions approach, was 0.059 µg/L, which indicated the PNEC of 0.0059 µg/L. In comparison, the highest concentration in seawater sampled from the Seto Inland Sea was 0.00034 µg/L, suggesting that the ecological risks posed by TPB-18 are currently low.

Occurrence of neonicotinoids and fipronil in estuaries and their potential risks to aquatic invertebrates.

This study aimed to evaluate and qualify field-based potential risks of seven neonicotinoid and phenylpyrazole (fipronil) insecticides on aquatic invertebrates, including estuary-resident marine crustaceans. One hundred and ninety-three estuarine water samples, with salinity ranging from 0.5 to 32.7, were collected from four estuarine sites in the Seto Inland Sea of Japan, in 2015-2018 and the insecticide levels were measured. Five neonicotinoid and fipronil insecticides were successfully identified, and their occurrence varied temporally. Marine crustaceans were simultaneously harvested every month from one of the estuarine water sampling sites in 2015-2017. Three predominant crustacean species, kuruma prawn (Penaeus japonicus), sand shrimp (Crangon uritai), and mysid (Neomysis awatschensis), were captured and their seasonal presence was species independent. A 96-h laboratory toxicity study with the insecticides using kuruma prawn, sand shrimp, and a surrogate mysid species (Americamysis bahia) indicated that fipronil exerted the highest toxicity to the three crustaceans. Using both toxicity data and insecticide occurrence in estuarine water (salinity ≥10, n = 169), the potential risks on the three marine crustaceans were quantified by calculating the proportion of mixture toxicity effects (Pmix). The Pmix of seven neonicotinoids on the crustaceans was less than 0.8%, which is likely to be too low to indicate adverse effects caused by the insecticides. However, short temporal detection of fipronil (exclusively in June and July) significantly affected the Pmix, which presented the maximal Pmix values of 21%, 3.4%, and 72% for kuruma prawn, sand shrimp, and mysid, respectively, indicating a significant effect on the organisms. As for estuarine water (salinity <10), some water samples contained imidacloprid and fipronil exceeding the freshwater benchmarks for aquatic invertebrates. The present study provides novel insights into the seasonally varying risks of insecticides to estuarine crustaceans and highlights the importance of considering whether ecological risk periods coincide with crustacean presence.

Physiological responses of eelgrass (Zostera marina) to ambient stresses such as herbicide, insufficient light, and high water temperature.

This study aimed to elucidate the biological responses of eelgrass (Zostera marina) to artificially induced stresses such as herbicide (Irgarol 1051, Irg) exposure, insufficient light, and high water temperature (27 ± 1.0 °C) by evaluating growth inhibition, photosynthetic activity, and metabolomic profiles. After 14 days, all treatments inhibited growth, but photosynthetic activity was only reduced in the Irg-exposed group. In the Irg-exposed and insufficient light groups, the metabolomic profiles were characterized by decreased levels of sugar (sucrose) and increased levels of amino acids such as glutamine, glycine, and leucine. Biochemical and ultrastructural analyses revealed that the loss of sugar-derived metabolic energy was compensated for by energy generated during autophagic protein degradation. Furthermore, the level of myo-inositol, which has various biological roles and participates in several cellular processes such as cell wall synthesis, stress response, and mineral nutrient storage, was markedly increased in the Irg-exposed and insufficient light groups. A combination of metabolomic analysis with other analyses such as measurement of photosynthetic activity might further elucidate the response of eelgrass to ambient stresses in the natural environment.

Toxicity of the biocide polycarbamate, used for aquaculture nets, to some marine fish species.

We investigated toxic effects of the antifouling biocide polycarbamate (PC) on marine fish by conducting acute, early-life stage toxicity (ELS), and embryo toxicity tests. Mummichog (Fundulus heteroclitus) 96-h LC50 values for hatched larvae (body weight about 2.0 mg) and juveniles (660 ±â€¯36 mg) were about 12 and 630 µg/L, respectively. The ELS test using mummichog embryos yielded a lowest-observed-effect concentration of 3.9 µg/L and a no-observed-effect concentration of 2.1 µg/L with growth as the most sensitive endpoint. The embryo toxicity test for spotted halibut (Verasper variegatus) revealed a 10-d EC50 of 8.1 µg/L with abnormality as an endpoint. During the ELS and embryo toxicity tests, morphological abnormalities (notochord undulation) were induced in the embryos. Biochemical and gene-expression analysis suggest that PC-induced morphological abnormalities involve disruption of lysyl oxidase-mediated collagen fiber organization, essential for notochord formation, and inhibition of gene expression related to notochord formation.

Sample treatment optimization for fish stool metabolomics.

Gut microbiota play an essential role in an organism's health. The fecal metabolite profiling content reflects these microbiota-mediated physiological changes in various organisms, including fish. Therefore, metabolomics analysis of fish feces should provide insight into the dynamics linking physiology and gut microbiota. However, metabolites are often unstable in aquatic environments, making fecal metabolites difficult to examine in fish. In this study, a novel method using gas chromatography-mass spectrometry (GC-MS) was developed and optimized for the preparation of metabolomics samples from the feces of the marine fish, red sea bream (Pagrus major). The preparation methodology was optimized, focusing on rinsing frequency and rinsing solvent. Feces (collected within 4 h of excretion) were rinsed three times with sterilized 2.5% NaCl solution or 3.0% artificial seawater (ASW). Among the 86 metabolites identified in the NaCl-rinsed samples, 57 showed superior recovery to that in ASW-rinsed samples, indicating that NaCl is a better rinsing solvent, particularly for amino acids, organic acids, and fatty acids. To evaluate rinsing frequency, fecal samples were rinsed with NaCl solution 0, 1, 3, or 5 times. The results indicate that three or more rinses enabled robust and stable detection of metabolites encapsulated within the solid fecal residue. Furthermore, these data suggest that rinsing is unnecessary when studying sugars, amino acids, and sterols, again highlighting the need for appropriate rinsing solvent and frequency. This study provides further insight into the use of fecal samples to evaluate and promote fish health during farming and supports the application of this and similar analyses to study the effects of environmental fluctuations and/or contamination.

The ovary organization in the marine limnodriloidin Thalassodrilides cf. briani (Annelida: Clitellata: Naididae) resembles the ovary of freshwater tubificins.

In Thalassodrilides cf. briani, the paired ovaries are inconspicuous and polarized structures with developmental gradient of germ cells along their long axis. The about 300 germ cells in the ovary are consolidated into one syncytial cyst and each cell is connected to a common and branched mass of cytoplasm via one stable cytoplasmic bridge. The germ cells differentiate their fate into nurse cells and oocytes. Only one oocyte grows in a given time; it gathers cell organelles and yolk and then it detaches from the gonad. Nurse cells appear to support oocytes development by providing with at least cell organelles. Such observations suggest ovary meroism. T. cf. briani, belonging to limnodriloidin naidids, has the same ovary organization as the representatives of tubificin naidids studied to date. This supports the concept of sister-group relations between Limnodriloidinae and Tubificinae. A similar ovary morphology is also known in several other groups of "microdrile" oligochaetes, which shows that this ovary type is the most widespread among this taxa. Moreover, living in marine or brackish-water sediments, T. cf. briani do not show any significant differences in their ovary structure and oogenesis with freshwater tubificins. This indicates its conservative character independent of the animal life environment.

Effect of taurine supplementation on hepatic metabolism and alleviation of cadmium toxicity and bioaccumulation in a marine teleost, red sea bream, Pagrus major.

This study was performed to unravel the mechanism of the beneficial action of taurine on marine teleost fish, red sea bream (Pagrus major), by analyzing the hepatic metabolism. Moreover, the ameliorative effects of the nutrient against cadmium toxicity and bioaccumulation were further evaluated. The fish were fed a diet containing 0 % (TAU0 %), 0.5 % (TAU0.5 %), or 5.0 % (TAU5.0 %) taurine for 40-55 days (d) and subjected to cadmium acute toxicity and bioaccumulation tests. Taurine deficiency in feed severely affected growth and the hepatic metabolic profiles of the fish, including a remarkable increase in myo-inositol, aspartate, and ß-alanine in the TAU0 % group, which indicates a complementary physiological response to taurine deficiency. For the acute toxicity test, fish were fed the test diets for 55 d and were then exposed to different dose of cadmium ranging from 0 to 5.6 mg/L for 96 h. Fish fed taurine had a higher tolerance to cadmium than those not fed taurine. For the bioaccumulation test, fish were fed the test diets for 40 d and then were chronically exposed to 0.2 mg/L of cadmium for 28 d followed by depuration for 21 d. Cadmium concentrations in the liver and muscle of fish fed TAU5.0 % were significantly lower than those of fish fed TAU0 % for the first 7 d of exposure and the first 7 d of elimination. Our findings suggest a possible mechanism for the beneficial role played by taurine and that the inclusion of taurine in fish aquaculture feed may reduce cadmium contamination of fish intended for human consumption.

Dietary taurine supplementation ameliorates the lethal effect of phenanthrene but not the bioaccumulation in a marine teleost, red sea bream, Pagrus major.

The present study was performed to evaluate the effect of dietary taurine on the hepatic metabolic profiles of red sea bream (Pagrus major) and on phenanthrene (a polyaromatic hydrocarbon) toxicity and bioaccumulation. The fish were fed a diet supplemented with 0% (TAU0%), 0.5% (TAU0.5%), or 5% (TAU5%) taurine for 40-55d and subjected to phenanthrene acute toxicity and bioaccumulation tests. Taurine deficiency in feed severely affected the hepatic metabolic profiles of fish, which indicated a complementary physiological response to taurine deficiency. For the acute toxicity test, fish were fed the test diets for 55d and were then exposed to 0-893µg/L phenanthrene for 96h. Tolerance to phenanthrene was significantly improved by 0.5% of taurine inclusion in feed relative to TAU0%, but not by 5.0% inclusion. Reduced glutathione in the liver, which acts as an oxygen-free radical scavenger, was associated with a reduction in the toxicity of phenanthrene. For the bioaccumulation test, fish were fed the test diets for 40d and were thereafter chronically exposed to 20µg/L phenanthrene for 13d followed by depuration for 3d. The activity of hepatic biomarker, ethoxyresorufin-O-deethylase, was increased by phenanthrene exposure in the taurine inclusion groups. However, phenanthrene concentrations in the liver and muscle of fish fed TAU5.0% tended to be higher than those of fish fed TAU0% and TAU0.5% during the exposure period. These results indicate that 0.5% of taurine inclusion in feed plays an important role in the alleviation of phenanthrene toxicity but not bioaccumulation. Furthermore, larger amount of taurine inclusion (TAU5%) did not show marked beneficial effects against phenanthrene exposure. This study provides insight about a major concern of environmental contaminants into aquatic environment and can be effectively used for improvement of aquaculture.

Photo-induced toxicity and oxidative stress responses in Tigriopus japonicus exposed to nitro-polycyclic aromatic hydrocarbons and artificial light.

Photo-induced toxicity is an important phenomenon in ecotoxicology because sunlight reaches many organisms in their natural habitats. To elucidate whether sunlight enhances the toxicity of nitro-polycyclic aromatic hydrocarbons (nitro-PAHs), the acute toxicities of 10 nitro-PAHs and the related compound 1-nitropyrene (1-NP) to Tigriopus japonicus were assessed in darkness or under light conditions. In addition, the relationships among the toxicity of 1-NP to T. japonicus, lighting condition, and the concentration of reactive oxygen species (ROS) formed were investigated in the presence or absence of the ROS scavenger ascorbic acid in the test solutions. Light irradiation increased the toxicity of all tested nitro-PAHs except 1,5-dinitronaphthalene. Among the compounds tested, 1-NP was the most phototoxic: it was more than 1000 times more toxic under the light conditions than in darkness. In contrast, at the same light levels, pyrene was not phototoxic. Light irradiation induced the generation of ROS in the 1-NP exposure groups, and the immobilization rate of T. japonicus increased with the amount of ROS produced. The addition of ascorbic acid to the test solutions suppressed both the generation of ROS and the light-induced immobilization of T. japonicus. To accurately assess the ecotoxicologic risk of nitro-PAHs, their overall photo-induced toxicity must be considered.

Cosmopolitan or Cryptic Species? A Case Study of Capitella teleta (Annelida: Capitellidae).

Capitella teleta Blake et al., 2009 is an opportunistic capitellid originally described from Massachusetts (USA), but also reported from the Mediterranean, NW Atlantic, and North Pacific, including Japan. This putatively wide distribution had not been tested with DNA sequence data; intraspecific variation in morphological characters diagnostic for the species had not been assessed with specimens from non-type localities, and the species status of the Japanese population(s) was uncertain. We examined the morphology and mitochondrial COI (cytochrome c oxidase subunit I) gene sequences of Capitella specimens from two localities (Ainan and Gamo) in Japan. Specimens from Ainan and Gamo differed from C. teleta from Massachusetts in methyl-green staining pattern, shape of the genital spines, and shape of the capillary chaetae; we concluded that these characters vary intraspecifically. Species delimitation analyses of COI sequences suggested that worms from Ainan and Massachusetts represent C. teleta; these populations share a COI haplotype. The specimens from Gamo may represent a distinct species and comprise a sister group to C. teleta s. str.; we refer to the Gamo population as Capitella aff. teleta. The average Kimura 2-parameter (K2P) distance between C. teleta s. str. and C. aff. teleta was 3.7%. The COI data indicate that C. teleta actually occurs in both the NW Atlantic and NW Pacific. Given the short planktonic larval duration of C. teleta, this broad distribution may have resulted from anthropogenic dispersal.

Evaluation of bioremediation potential of three benthic annelids in organically polluted marine sediment.

This study aimed to evaluate the possible remedial effects of three marine benthic annelids on organically polluted sediments from the waters of Hatsukaichi Marina, Hiroshima, Japan. Two polychaetes, Perinereis nuntia and Capitella cf. teleta, and an oligochaete, Thalassodrilides sp., were incubated in sediments for 50 days. Their effects on physicochemical properties such as organic matter (loss on ignition), redox potential (Eh), acid volatile sulfides (AVS), and degradation of polycyclic aromatic hydrocarbons (PAHs) were assessed. The polychaetes P. nuntia and C. cf. teleta significantly increased Eh level and decreased AVS level compared with the oligochaete Thalassodrilides sp. and control (without benthic organisms). Total PAH concentration significantly decreased from the initial level with all three groups; Thalassodrilides sp. had a marked ability to reduce PAHs in sediment. These results indicate that benthic organisms have species-specific remediation properties and ecological functions in organically polluted sediments.

Transcription of a novel P450 gene varies with some factors (pollutant exposure, temperature, time, and body region) in a marine oligochaete (Thalassodrilides sp.).

Cytochrome P450 (CYP) enzymes play important roles in the metabolism of exogenous compounds such as polycyclic aromatic hydrocarbons (PAHs). A novel, full-length CYP gene (CYP4V30) was identified in the oligochaete Thalassodrilides sp. CYP4V30 mRNA expression was studied in worms exposed to PAH-polluted (Σ16PAHs; 37441ng/g dry weight) or unpolluted (Σ16PAHs; 19ng/g dry weight) sediment. CYP4V30 expression was much higher in worms exposed to contaminated sediments than in those exposed to unpolluted sediments at some temperatures (20 and 25°C) and exposure durations (11-fold increase at 20°C, 10-day exposure), but not at 15°C or other exposure durations (P<0.05). CYP4V30 mRNA expression was higher in the middle of the body than in the posterior (P<0.05). The variation in transcriptional response with exposure time, temperature, and body region indicates that these factors should be considered when monitoring marine sediment pollution.

Differences in the ability of two marine annelid species, Thalassodrilides sp. and Perinereis nuntia, to detoxify 1-nitronaphthalene.

Bioremediation is a promising method for remediating environmentally polluted water. We investigated the abilities of two benthic annelid species to biotransform 1-nitronaphthalene, a nitrated polycyclic aromatic hydrocarbon. We used an oligochaete, Thalassodrilides sp. (Naididae), collected from the sediment beneath a fish farm and a polychaete, Perinereis nuntia, which was obtained from a commercial source. Populations of both organisms were exposed to 1400 µg L(-1) of 1-nitronaphthalene in seawater for 3 days in the dark at 20 °C. The concentration of the pollutant decreased to 12 µg L(-1) in the seawater containing the Thalassodrilides sp. and to 560 µg L(-1) in the seawater containing P. nuntia. The 1-nitronaphthalene concentration in the bodies of the animals increased from 12 to 94 µg kg(-1) in Thalassodrilides sp. and from 0.90 µg kg(-1) to 38,000 µg kg(-1) in P. nuntia. After 3 days, 99% and 40% of the 1-nitronaphthalene had been biotransformed in the Thalassodrilides sp. and P. nuntia experimental groups, respectively. We then tested the acute toxicity of residual 1-nitronaphthalene from the same water using mummichog (fish) larvae. After the larvae had been exposed for 96 h, the percentage of apparently unaffected larvae remaining was 83.3% in Thalassodrilides sp. group but only 16.7% in the P. nuntia group. Clearly, of the two species we studied, Thalassodrilides sp. had a superior ability to convert 1-nitronaphthalene into substances that were nontoxic to mummichog larvae. Therefore, we recommend the use of this species for bioremediation of chemically polluted sediments.