Toxicity Of Tributyltin Research Articles

Diethylphosphine oxide (DEPO): high-yielding and facile preparation of indolones in water.

[reaction: see text] Indolones are prepared in excellent yield at 80 degrees C in water by radical reaction (aryl radical formation, hydrogen atom abstraction, cyclization, and rearomatization) mediated by the reagent diethylphosphine oxide (DEPO). The reaction features V-501 as a water-soluble initiator; no other additives are needed. The process proceeds at a much lower temperature than is required for efficient reaction with toxic tributyltin hydride in benzene and permits significantly higher isolated yields than the corresponding reaction mediated by ethylpiperidine hypophosphite (EPHP).

Urban soil pollution and the playfields of small children

The chemical composition of urban surface soil in Tromso, northern Norway has been mapped to describe the environmental load of toxic elements in different parts of the city. Surface soil samples were collected from 275 locations throughout the city center and nearby suburban areas. Natural background concentrations were determined in samples of the local bedrock. Surface soil in younger, suburban parts of the city shows low concentrations of heavy metals, reflecting the local geochemistry. The inner and older parts of the city are generally polluted with lead (Pb), zinc (Zn) and tin (Sn). The most important sources of this urban soil pollution are probably city fires, industrial and domestic waste, traffic, and shipyards. In this paper two different approaches have been used. First, as a result of the general mapping, 852 soil and sand samples from kindergartens and playgrounds were analyzed. In this study concentrations of arsenic (As) up to 1800 ppm were found, most likely due to the extensive use of CCA (copper, chromium, arsenic) impregnated wood in sandboxes and other playground equipment. This may represent a significant health risk especially to children having a high oral intake of contaminated sand and soil. Secondly a pattern of tin (Sn) concentrations was found in Tromso city with especially high values near shipyards. Further investigation indicated that this pattern most probably reflected the use of the highly toxic tributyltin (TBr). Thus determination of total Sn in surface soils could be a cost-effective way to localize sources of TBT contamination in the environment.

Fluorescence X-ray microscopy on hydrated tributyltin-clay mineral suspensions

Using the scanning transmission X-ray microscope at ID21 beamline of the ESRF in fluorescence mode, we mapped tin at a bulk concentration of 1000 μg(Sn)/ml within hydrated tributyltin (TBT) - clay mineral (Kaolinite) dispersion with sub-300 nm spatial resolution. Using the L absorption edges of tin at 3929, 4156 and 4465 eV fluorescence radiation was excited in tin atoms with incident photon energies of 4 and 4.5 keV. When using 4 keV radiation, only tin fluorescence is excited. For 4.5 keV X rays, both the fluorescence of tin and calcium (which is present in the solid phase) can be measured. Methodologically, we were interested in assessing and proving the possibilities and limitations of fluorescence mapping using the L absorption edges of tin, where the fluorescence yield is significantly lower compared to other elements with their K edges in the same energy range. Scientifically, organotin-clay mineral interactions are of environmental concern because this factor influences significantly the distribution of toxic TBT in the aquatic system. On one hand, the half-life of TBT deposited to the sediment phase increases, and consequently the time of its bioavailability. On the other hand, the adsorption process is reversible, which means that contaminated sediments can act as a source of pollution. The adsorption and desorption effects can be studied directly with high spatial resolution and brought into connection to the surface properties of the clay mineral under study as well as to other experimental parameters, like pH or salinity.

Assessment of adsorption behavior of dibutyltin (DBT) to clay-rich sediments in comparison to the highly toxic tributyltin (TBT)

The sorption behavior of dibutyltin (DBT) to four types of natural clay-rich sediments as a function of pH and salinity was studied. The strongest affinity of DBT was found to the montmorillonite-rich sediment, which is characterized by the highest specific surface area and cation exchange capacity of the four used sediments. K d values range between 12 and 40 (l/kg) on simulated marine conditions (pH 8, salinity 32‰). A maximum of DBT adsorption was found at a salinity of 0‰ and pH 6. Desorption occurred over the entire studied pH range (4–8) when contaminated sediments interact with butyltin-free water. The maximum of desorption coincided with the minimum of adsorption, and vice versa. The results of DBT adsorption are compared with tributyltin (TBT), and the mechanism of the adsorption process is discussed.

Toxicity assessment of sediments containing tributyltin around Hong Kong harbour

Rather high levels of tributyltin (TBT) in sediments were found in certain areas around the Hong Kong coastline. Sediments from two contaminated sites (Tsing Yi and Yam O) and two clean sites were used to study the release of TBT contaminants from resuspended sediment to the water column by elutriate tests. The chemical analysis data of elutriates were compared with the effective or lethal concentrations from the toxicity tests of spiked solution using marine microalga ( Dunaliella tertiolecta) and benthic invertebrate ( Melita koreana) to assess the potential ecotoxicological impacts arising from the dredging work. Concentrations of TBT in filtered sediment elutriates were mostly below 0.002 μg/l which suggested that very little of TBT was released in soluble form. The lethal toxicity of TBT for the invertebrate expressing as 10 day-LC 50 was 2.31 μg/l for TBT and the alga expressing as 48 h-EC 50 was 0.46 μg/l. The results of this evaluation demonstrated that the release of TBT from two contaminated sites during dredging was unlikely to attain the effective or lethal concentrations on the two test species.

Adsorption behavior of toxic tributyltin to clay‐rich sediments under various environmental conditions

The adsorption and desorption behavior of tributyltin (TBT) from aqueous solution to clay-rich sediments was studied under various conditions (pH, salinity) using the batch technique. Sediments containing illite, kaolinite, and montmorillonite in different proportions were used as sorbent materials. Several physicochemical parameters of the sediments (e.g., Brunauer-Emmett-Teller [BET] surface area, cation exchange capacity [CEC], total organic carbon [TOC]) were evaluated to assess the influence of sediment characteristics to the adsorption capacity for TBT Adsorption isotherms were linear over the concentration range of 100 to 1,000 ng(Sn)/ml. The adsorption coefficient (Kd) values range from 29 to 70 at the pH value generally found in marine systems (pH 8). The adsorption capacity shows a maximum in the range of pH 6 and 7. Salinity is also an important factor in controlling TBT adsorption. The strongest adsorption was observed at salinity of 0/1000, and it strongly decreases with increasing salinity. The adsorption mechanism is controlled by the properties of the clay minerals as well as the aquatic chemistry of TBT. Desorption takes place over the studied pH range (4-8) when contaminated samples interact with TBT-free water at given experimental conditions.

Differences in the acute toxicities of tributyltin between the Caprellidea and the Gammaridea (Crustacea: Amphipoda)

Tests for the acute toxicity of tributyltin (TBT) were conducted on amphipod crustaceans collected from Otsuchi Bay, Japan. Five species of caprellids and three species of gammarids, which belong to a closely related ecological niche, were used for the exposure experiments at seven test concentrations (0, 0.001, 0.01, 0.1, 1, 10 and 100 μg TBTCl/l) for 48 h at 20°C. The 48-h LC 50 values of the caprellids were 1.2–6.6 μg TBTCl/l, and these were significantly lower than those of the gammarids (17.8–23.1 μg TBTCl/l). This suggests that caprellids are more sensitive to TBT than gammarids. Furthermore, the proportions of TBT and its derivatives, dibutyltin (DBT) and monobutyltin (MBT), were measured in the amphipods collected from Otsuchi Bay. In the caprellids, TBT was the predominant compound, accounting for 72% of the total butyltin which reflected the butyltin ratio in seawater, while in the gammarids, TBT's breakdown products (DBT and MBT) predominated, accounting for 75% of the total butyltin. This difference suggests that caprellids may have lower metabolic capacity to degrade TBT than gammarids. Therefore, the difference in sensitivity to TBT among the amphipods is thought to be related to the species-specific capacity to metabolize TBT.

Biotransformation and Disposition of Testosterone in the Eastern Mud Snail Ilyanassa obsoleta

Elevated testosterone levels have been reported to be associated with imposex (pseudohermaphroditism), the superimposition of male characteristics such as a penis and vas deferens on female gonachoristic snails. Tributyltin (TBT), a marine biocide in anti-fouling paints, is a known causal agent of imposex. Evidence suggests that imposex is elicited by TBT-mediated changes in the biotransformation and disposition of testosterone. To identify potential targets of TBT in gastropod species susceptible to imposex, biotransformation and disposition of testosterone in normal individuals must first be characterized. Nonimposex mud snail, Ilyanassa obsoleta, readily extracted [14C]testosterone, added to aqueous media, and converted the testosterone to at least five apolar conjugates designated AP1 through AP5. All were retained by the organisms. No significant amount of [14C]testosterone was retained or eliminated as polar metabolites. Following enzymatic hydrolysis of the most abundant metabolite (AP1), free fatty acids and [14C]testosterone were liberated. Furthermore, AP1 was produced when homogenized snail tissue was incubated with [14C]testosterone and oleoyl coenzyme A or palmitoyl coenzyme A. These results indicate that AP1, which represents over 70% of the testosterone biotransformation products, is a fatty acid ester of testosterone. Apolar metabolites AP2–AP5 might represent testosterone derivatives that are multiply conjugated to fatty acid molecules. Fatty acid conjugates of testosterone have not been previously described in the gastropods. The esterification of testosterone to fatty acids might be a mechanism where by steroid titers are regulated and could represent a target of TBT toxicity.

TBT effects on the larvae of Ruditapes decussatus

The effects of sublethal tributyltin (TBT) concentrations on the growth and development of Ruditapesdecussatus larvae were studied. Veliger larvae of R. decussatus were exposed to TBT nominal concentrations of 25, 50, 75 and 100 ng Sn l−1 in the water for a period up to 13 d. Larval growth and development were chosen as endpoints for evaluation of TBT toxicity. Growth of R. decussatus larvae was severely affected by TBT concentrations (25–100 ng Sn l−1). A 3- to 6-fold reduction growth was observed in these early larval stages. Furthermore, R. decussatus larvae exposed to TBT did not develop further than D-larvae while the unexposed ones reached the umbonated stage.

Review of the Persistence, Bioaccumulation and Toxicity of Tributyltin in Aquatic Environments in Relation to Canada's Toxic Substances Management Policy

Abstract The extremely toxic antifouling pesticide tributyltin (TBT) was regulated in many countries in the 1980s and 1990s. The regulations have been successful in reducing the toxic threat posed by TBT in many locations around the world. However, there are also many locations at which recovery has not been seen, even 10 years after regulation. Because of continuing concern about the environmental hazards of TBT, the International Maritime Organization proposes to prohibit all antifouling uses of TBT by 2003, and the presence of TBT on ship hulls by 2008. Canada has recently announced a prohibition on the use of organ-otin antifouling paints by January 1, 2003. This article reviews the persistence, bioaccumulation and toxicity of TBT in aquatic environments, and concludes that TBT meets all such criteria for designation as a Track 1 substance under Canada's Toxic Substances Management Policy, necessitating measures to virtually eliminate it from the Canadian environment. Because of the long persistence of TBT in sediment, there may be a "legacy problem" in sediments in some locations in Canada for perhaps 20 to 30 years after a total ban.

A review of organotin regulatory strategies, pending actions, related costs and benefits

Achieving consensus on equitable and effective national and global regulation(s) for the use of organotins as biocides in antifouling boat bottom paints has proven to be very complex and difficult for a variety of reasons as discussed in this paper. There appears to be broad agreement among stakeholders about the effectiveness of tributyltin (TBT) in antifouling paints. A draft Assembly Resolution prepared by the Marine Environmental Protection Committee (MEPC) of the International Maritime Organization (IMO) to propose a global ban on the use of organotins in antifouling paints was approved by the IMO at its 21st regular session (November 1999). In approving the Resolution, the Assembly agreed that a legally binding instrument (global convention--an international treaty) be developed by the Marine Environmental Protection Committee that should ensure by 1 January 2003, a ban on the application of tributyltin (TBT)-based antifouling paints; and 1 January 2008 as the last date for having TBT-based antifouling paint on a vessel. The Assembly also agreed that a diplomatic conference be held in 2001 to consider adoption of the international legal instrument. Monitoring, policing, enforcement, fines and record-keeping are yet to be defined. In addition, the MEPC has also proposed that IMO promotes the use of environmentally-safe anti-fouling technologies to replace TBT. Existing national regulations in the US and Europe have: (1) restricted the use of TBT in antifouling boat bottom paints by vessel size (less than 25 m in length), thus eliminating TBT from the smaller and recreational vessels that exist in shallow coastal waters where the impacted oysters species grow; (2) restricted the release rates of TBT from co-polymer paints; and (3) eliminated the use of free TBT in paints. The present movement toward a global ban suggests that the above regulatory approach has not been sufficient in some countries. Advocates of the ban cite international findings of: (1) higher levels of TBT in surface waters of ports and open waters; (2) imposex still occurring and affecting a larger number of snail species; (3) TBT bioaccumulation in selected fisheries; and (4) the availability of 'comparable' alternatives (to TBT) with less environmental impact. The global ban has been absent of a policy debate on the: (1) lack of 'acceptable and approved' alternatives in many nations; (2) appreciation of market forces in nations without TBT regulations; (3) full consideration of the economic benefits from the use of TBT; (4) 'acceptance' of environmental impacts in marinas, ports and harbors; and (5) realization of the 'real' time period required by ships for antifoulant protection (is 5-7 years necessary or desirable?). Estimates of fuel savings range from $500 million to one billion. In assessing the environmental impact from TBT, there are two sources: the shipyard painting vessels and the painted vessel itself. Today vessels can be painted with regulated or banned antifouling materials by boatyards in a country that does not have TBT regulations and subsequently travel in international and regulated national waters and thus bringing the impact back to the country which was trying to prevent it. Worse, local and national regulations for TBT have proven to be the antithesis of the popular environmental cliché--'Think Globally and Act Locally.' Legislative policies enacted by 'regulated' countries to regulate the use of TBT to protect (their) local marine resources have subsequently had far reaching environmental and economic impacts which have in essence transferred TBT contamination to those countries least able to deal with it. Market forces are selective for cheap labor and cheap environments. 'Unregulated' countries have unknowingly accepted the environmental and human health risks to gain the economic benefits from painting TBT on ships. (ABSTRACT TRUNCATED)

Assessment of risks on US Pacific Coast otters feeding on bivalves and associated tributyltin

Potential risks to US Pacific Coast sea otters were assessed using tributyltin (TBT) bivalve data and sea otter food ingestion rates and body weights. TBT toxicity data (e.g. no observed adverse effects levels and lowest observed adverse effects levels) for a surrogate wildlife species were used after applying an uncertainty factor using Environmental Protection Agency guidance. The toxicological effects' endpoints were based on immune suppression effects. Potential risk to sea otters was considered using hazard quotients to determine whether the estimated dose exceeded the toxic dose. Populations of sea otters were evaluated as well as individuals that frequented marinas. Risks are not predicted for greater than 99% of the sea otter populations which feed on prey in coastal waters. If we assume that the few individual otters seen in marinas of California and Alaska are feeding on bivalves living in marinas, and if we make conservative assumptions about the percent of marina bivalves in their diet, risks are not predicted for three of the four immune suppression effect endpoints.

Toxicity of butyltin, phenyltin and inorganic tin compounds to sulfate-reducing bacteria isolated from anoxic marine sediments

The toxicity of butyltin, phenyltin and inorganic tin compounds to three pure strains of sulfate-reducing bacteria (SRB), isolated from a tributyltin (TBT)-polluted sediment, was determined. The isolated strains were identified as belonging to the genus Desulfovibrio. A new toxicological index (GR25) was developed to assay the toxicity of organotin compounds. Deleterious effects on suspended anaerobic cell cultures were observed for concentrations ranging between 500 and 600 µM for tin tetrachloride, 55 and 260 µM for triorganotins, 30 and 90 µM for diorganotins, and 1 and 6 µM for mono-organotins. Whereas the number of substituents influenced the toxicity of organotins, the type of substituent (butyl or phenyl) proved to have little or no impact. Trisubstituted compounds (tributyl- and triphenyl-tin) were less toxic to these strains of SRB than the monosubstituted forms (monobutyl- and monophenyl-tin). This is the opposite trend to that currently reported for aerobic organisms. Under the given anoxic conditions, the toxicity of organotin compounds obtained yielded a significant negative correlation with the total surface area (TSA) of the tested molecules. Comparison of the TBT toxicity data observed for different microbial groups suggests that the tolerance of bacteria to organotin compounds might be related to organotin–cell wall interactions as well as to aerobic or anaerobic metabolise pathways. Copyright © 2000 John Wiley & Sons, Ltd.

Tributyltin induces cytogenetic damage in the early life stages of the marine mussel,Mytilus edulis

Using an integrated approach, the genotoxic potential of bis(tri-n-butyltin), an antifouling agent known to disrupt endocrine system in marine invertebrates, has been evaluated in the embryo-larval stages of the edible mussel, Mytilus edulis. While evaluating the genotoxic potential, the toxicity of tributyltin was also taken into account by determining the maximum tolerated dose. The study suggested that tributyltin is capable of inducing cytogenetic damage (sister chromatid exchanges and chromosomal aberrations) in this target species. The study emphasises the need for further investigations of the potential genotoxic effects of this and other endocrine disrupters on ecologically relevant aquatic invertebrates, which contribute to the maintenance of ecosystems and that could potentially be harmful to human health via the food chain.

Tributyltin induces cytogenetic damage in the early life stages of the marine mussel, Mytilus edulis

Using an integrated approach, the genotoxic potential of bis(tri-n-butyltin), an antifouling agent known to disrupt endocrine system in marine invertebrates, has been evaluated in the embryo-larval stages of the edible mussel, Mytilus edulis. While evaluating the genotoxic potential, the toxicity of tributyltin was also taken into account by determining the maximum tolerated dose. The study suggested that tributyltin is capable of inducing cytogenetic damage (sister chromatid exchanges and chromosomal aberrations) in this target species. The study emphasises the need for further investigations of the potential genotoxic effects of this and other endocrine disrupters on ecologically relevant aquatic invertebrates, which contribute to the maintenance of ecosystems and that could potentially be harmful to human health via the food chain. Environ. Mol. Mutagen. 35:343–350, 2000 © 2000 Wiley-Liss, Inc.

A Probabilistic Ecological Risk Assessment of Tributyltin in Surface Waters of the Chesapeake Bay Watershed

The goal of this study was to conduct a probabilistic ecological risk assessment for tributyltin (TBT) in surface waters of the Chesapeake Bay watershed. Ecological risk was characterized by comparing the probability distributions of environmental exposure concentrations with the probability distributions of species response data determined from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Tributyltin exposure data from the Chesapeake Bay watershed were available from over 3600 water column samples from 41 stations in nine basins from 1985 through 1996. Most of the stations were located in the Virginia waters of Chesapeake Bay, primarily the James, Elizabeth and York Rivers. In Maryland waters of the Bay, various marina, harbor and river systems were also sampled. As expected, the highest environmental concentrations of tributyltin (based on 90th percentiles) were reported in and near marina areas. The sources of TBT causing these high concentrations were primarily boat hulls and painting/depainting operations. Lower concentrations of TBT were reported in open water areas, such as the Potomac River, Choptank River and C and D Canal, where the density of boats was minimal. Temporal data from a ten year data base (1986-1996) from two areas in Virginia showed that TBT water column concentrations have declined since 1987 legislation prohibited the use of TBT paints on recreation boats (<25 m).Acute saltwater and freshwater TBT toxicity data were available for 43 and 23 species, respectively. Acute effects for saltwater species were reported for concentrations exceeding 420 ng/L; the lowest acute value for a freshwater species was 1110 ng/L. The acute 10th percentiles for all saltwater and freshwater species were 320 and 103 ng/L, respectively. The order of sensitivity from most to least sensitive for saltwater trophic groups and corresponding acute 10th percentiles were as follows: zooplankton (5 ng/L), phytoplankton (124 ng/L), benthos (312 ng/L) and fish (1009 ng/L). For freshwater species, the order of sensitivity from most to least sensitive trophic groups and corresponding acute 10th percentiles were: benthos (44 ng/L), zooplankton (400 ng/L), and fish (849 ng/L). Chronic data for both saltwater and freshwater species were limited to a few species in each water type. Based on these limited data, the saltwater and freshwater chronic 10th percentiles were 5 and 102 ng/L, respectively. Limited mesocosm and microcosm studies in saltwater suggested that TBT concentrations less than 50 ng/L did not impact the structure and function of biological communities.The saltwater acute (320 ng/L) and chronic (5 ng/L) 10th percentiles were used to determine ecological risk because all exposure data were from saltwater areas of the Chesapeake Bay watershed. Highest ecological risk was reported for marina areas in Maryland waters of Chesapeake Bay and for areas in Virginia such as the Elizabeth River, Hampton Creek and Sarah Creek. Low ecological risk was reported for areas such as the Potomac River, Choptank River, C and D Canal and Norfolk Harbor. Regulation of TBT on recreational watercraft in 1987 has successfully reduced water column concentrations of this organometallic compound. However, various studies have showed that TBT may remain in the sediment for years and continue to be source for water column exposures.

Bioaccumulation and toxicity of tributyltin to a burrowing heart urchin and an amphipod in spiked, silty marine sediments.

The presence of tributyltin (TBT) in silty sediments is regarded as a long-term threat to marine and estuarine environments due to its persistence. The bioaccumulation kinetics and toxicity of TBT in the deposit-feeding heart urchin Echinocardium cordatum was studied in silty sediment spiked with TBT and equilibrated prior to the 28-d exposure. An additional 10-d acute toxicity test was carried out with the burrowing amphipod Corophium volutator in the same sediment. Because E. cordatum has a low lipid content and apparently high elimination and metabolic rates, only a moderate degree of TBT bioaccumulation was observed, with biota-sediment accumulation factors (BASFs) of 0.09 to 0.21 (dry weight basis) and biota accumulation factors (BAFs) of 180 to 843 (wet weight basis). The lethal body residue in E. cordatum (soft tissue and skeleton) was 0.8 to 3.4 nmol TBT+ /g wet weight which, considering the differences in lipid content, is comparable to data on other taxonomic groups. For E. cordatum and C. volutator, the LC50s for pore water (222 and 329 ng Sn/L) were also close to reported values for aquatic and benthic organisms. The TBT concentrations in the pore water of the silty sediment were much lower than might be expected from the octanol-water partition coefficient. The measured sediment-water partitioning coefficient Kp was 8,700 L/kg dry weight. Consequently, toxicity was observed at a relatively high TBT concentration in the bulk sediment with LC50s for E. cordatum and C. volutator of 1,594 and 2,185 ng Sn/g dry weight, respectively. The results show that TBT is highly toxic to the benthic species investigated and sorption in the silty sediment strongly reduced the bioavailability of the compound.

Effects of an Organic Pollutant (Tributyltin) on Genetic Structure in the Pacific Oyster Crassostrea gigas

Within the overall context of coastal ecosystem monitoring, the effects of an organic pollutant (i.e. tributyltin) on the genetic structure of the Pacific oyster Crassostrea gigas along Brittany (France) coasts were studied in order to identify specific genetic indicators. Contamination experiments were conducted using two concentrations of tributyltin (TBT). Electrophoretic analyses focused on six enzyme loci and the results were analysed to discern allozyme differences between samples. The survival curves obtained clearly reveal the high toxicity of TBT on adult oysters. Electrophoretic data also highlighted the existence of allozymes which can be used as putative genetic indicators of TBT contamination. It would appear that the following enzyme systems, aspartate-amino-transferase (Aat-2), adenylate kinase (Ak) and phosphoglucomutase (Pgm) are involved in the main physiological processes affected by tributyltin; allozymes of these loci are characterized by frequencies which vary significantly between TBT-resistant and more TBT-sensitive adults. These data reflect the adaptive nature of certain allozymes and show that relatively simple methods associated with an appropriate biological material may be a powerful tool to assess the effects of pollutants on marine invertebrates.

Transgenerational toxicity of tributyltin and its combined effects with polychlorinated biphenyls on reproductive processes in Japanese medaka (Oryzias latipes)

AbstractJapanese medaka (Oryzias latipes) were fed daily on one of four diets containing tributyltin (TBT), PCBs, a combination of TBT and PCBs, or a control diet (with nothing added). Contaminant doses were 1 μg/g body weight per day for 3 weeks. The combination of TBT and PCB showed additive effects on the spawning of medaka, resulting in a significant reduction in spawning frequency, and on the number of spawned eggs and fertilization success when compared with effects in fish fed either a TBT or PCB diet. The adverse effects on the reproductive success of medaka may have been due to endocrine disruption caused by accumulation of both TBT and PCB. The TBT treatment significantly reduced embryo and larval survival from eggs (279 ng TBT/g), which were spawned from females containing 2,390 ng TBT/g body weight from the TBT diet. This result indicates transgenerational toxicity. The PCB diet caused fewer adverse effects than the TBT diet with respect to spawning frequency, egg survival, hatching, and swim‐up success of larvae. When both TBT and PCB were in the diet, there were additive effects on spawning success as noted above but antagonistic effects on embryological success of eggs and swim‐up success of larvae.

Effects of tributyltin on medaka ( Oryzias latipes) embryos at different stages of development

Potential mechanisms of action for the toxicity of tributyltin (TBT) were studied in the freshwater fish embryos of medaka ( Oryzias latipes). Toxic concentrations of TBT have been found in estuaries and freshwater systems, presumably due to their use as biocides in boat, antifoulant paints and in industry for plastics production. Medaka embryos were exposed to a single concentration of TBT at developmental stages that corresponded to the formation of structures and/or organs which might be potential targets. Times of exposure included day 0, oviposition, day 3, completion of somite formation, and day 5, liver formation. Endpoints for evaluating toxicity were acute embryo lethality (96 h), rate of embryo development, hatching success, gross abnormalities, as well as hatchling eye diameter and number of somites. The clear chorion of medaka embryos allowed staging and in ova observations. Results showed that the acute toxicity of TBT was stage related. The 96 h LC 50 (LC 50: lowest concentration to cause 50% lethality in the test population) for embryos exposed on day 0 was 159 nM, which was lower than that for days 3 and 5, 360 and 340 nM, respectively. Subchronic endpoints showed that toxicity was concentration related and that embryos exposed on day 0 were more sensitive than those exposed on days 3 and 5. Lowest observable effect levels (LOELs) for hatching success were 36 nM for day 0 and 143 nM for days 3 and 5. LOELs for the combined effects of hatching success and gross abnormalities were 36 nM for day 0 and 71 nM for days 3 and 5. Developmental rate was slowed by TBT in a concentration-related manner; however, embryos treated with 36 and 71 nM were able to recover and hatch at the same time as controls. Types of gross abnormalities were similar regardless of day of exposure and consisted of tails bent at the tip, curled, and/or shortened. These abnormalities corresponded with statistically significant reductions in numbers of somites in all three age groups exposed to 71 nM ( P<0.05). Although day 0 embryos were the most sensitive, the similar abnormalities for all 3 days of exposure indicated that TBT's toxicity was not due to effects on an age-dependent target but one present throughout embryo development.