abstracts for
2 Toxicology

The Minamata Bay remedial project, which commenced in 1977 was completed in 1990. 1.5 million m3 of mercury contaminated sediment were treated by careful dredging and confined reclamation. A contaminated area of 2 million m2 in Minimata Bay was decontaminated.

During this large project, we have faced several technical problems. Some of the experiences are expected to be useful for planning remedial works of other areas. The following topics are presented with technical details:

1. initial distribution of mercury in the bottom sediment,
2. monitoring system design and monitoring committee,
3. dredging work with specially designed vessels,
4. sand capping over reclaimed sediment for confinement,
5. residual mercury after dredging.

Economic considerations were important, but we gave a higher priority to safety. For the remediation, we had to use every possible technique in order to minimize secondary pollution.

Late in 1953 a severe neurological disorder first was recognized among inhabitants in the vicinity of Minamata Bay, situated in southwestern Kyushu in Japan. By 1956 the outbreak had reached epidemic proportions; 111 cases were found as of the end of 1960, and 41 deaths were reported as of August 1965 (Figs. 1 and 2). These cases were caused by eating abundantly the fish and shellfish from Minamata Bay and the neighboring sea, except for 19 congenital cases born of mothers who had eaten the same fish. Besides human beings, cats and water fowl living near the bay succumbed to the disease. Cats and rats fed on the fish and shellfish from the bay developed the same symptoms and findings as animals spontaneously affected. Clinical features were cerebellar ataxia, constriction of visual fields, dysarthria, etc.; congenital cases were accompanied by disturbance of physical and mental development. Pathological findings were regressive changes in the cerebellum and the cerebral cortices, and the most conspicuous changes were noticed in the cerebellum and the calcarine cortex. These clinico-pathological features resembled the alkylmercury poisoning already reported. Abnormal mercury content was proved in the fish, shellfish, and muds from the bay and in organs of necropsy cases and cats which had succumbed to the disease. Although no mercury was extracted with organic solvents from the powder or the boiled fluids of the fish and shellfish from the bay, some mercury compound in the hydrolysate with HCI and the digest with pepsin of the fish and shellfish was steam-distilled and the mercury compound in the distillates was extracted with organic solvents. It was an organomercury compound.

In 1956, symptoms of a strange human disease were reported in Minamata City, Kumamoto Prefecture, Japan. After careful investigation, the disease, the infamous Minamata disease, was attributed to poisoning by methyl mercury compounds.

In 1965, victims of methyl mercury poisoning were found along the Agano River, Niigata Prefecture. This was called the Niigata Minamata disease or the second Minamata disease. Mercury in industrial wastewater discharged into public waters was being concentrated in fish and shellfish were poisoned. To prevent environmental mercury pollution and new cases of poisoning, Japan instituted various countermeasures.

At present, no effluents containing mercury are discharged into public waters, but there are still mercury- poisoned fish and shellfish. The bottom material is suspected of being responsible, and measures to remove or to isolate bottom sediments have been seriously discussed. This paper outlines the measures taken against mercury pollution in Japan and the mercury-contaminated sludge cleanup project in Minamata Bay.

Every day, man creates new processes and materials whose properties are not fully known and are sometimes toxic to him and the environment. One of the worst cases was in Minamata Bay, Japan where a fatal accident occurred due to mercury pollution. The accident was unique in many aspects thus forcing the establishment of a new decontamination process for polluted areas. Two mercury polluted sites, the Ottawa River, Canada and Minamata Bay (Yatsushiro Sea), Japan, have been investigated to establish a fundamental approach for decontamination with special emphasis on natural and artificial processes and their problems. Artificial decontamination on bottom sediments has primarily cleaned-up Minamata Bay and the near-by Yatsushiro Sea considerably, an acceleration of the natural processes by 31.5 years. The surrounding area will be fully cleaned-up by natural forces, following the artificial work, by 2011 AD (or 20 years from now). This means that the natural decontamination has a half-life of 9.5 years in Yatsushiro Sea. For the Ottawa River, only natural processes were applied to clean-up the river system. It took 5 years for physical components to be decontaminated (a half-life of 1.20 years) while it took a longer period for biological components. This last finding was also true for Minamata Bay. This delay may be due to the longer life span of the biota and their efficient processes of bioaccumulation from diluted surrounding water. Based on the findings herein, a combination of both artificial and natural decontamination methods is recommended in consideration with the given environmental conditions.

Nearly three decades have passed since the first outbreak of Minamata disease (methyl mercury poisoning). Since then, the Japanese government has taken the position that mercury contamination is occurring only within Minamata Bay, and commercial and sport fishing has been prohibited only within the bay. However, about 30 tons of mercury has quietly been moving into the Yatsushiro Sea, although most of the mercury (150 tons) which was released (and which induced the disease) has been deposited with bed sediments within Minamata Bay. Observations from 1975 to 1980 confirm that the dispersion of the mercury from the bay into Yatsushiro Sea is imminent and that the average concentration of mercury in bed sediments has increased 315% between 1975 and 1980 in the Yatsushiro Sea.

At Minamata Bay in Japan, more than 100 people lost their lives and many thousands more were permanently paralyzed from eating mercury contaminated fish. In the long history of water pollution, this was the first known case where the natural bioaccumulation (in fish) of a toxicant from an industrial wastewater killed a large number of human beings. The mercury, discharged from a factory, was deposited on the bottom of the Bay and has remained there since the 1950's.

The fate of the mercury was traced by measuring 268 mercury concentrations in the surface sediments at Yatsushiro Sea (outside of the Bay) during the last 14 years. Twenty-four sampling stations were established to collect samples at the same location every year. Samples were analyzed for total mercury concentrations.

The concentrations of mercury in the surface sediments at the Sea were not alarming. Only 33 samples exceeded a mercury concentration of 1 ppm. The dispersion of the mercury from the Bay, however, was clearly documented with the data. On average, 3.7 tons of the mercury was transported outside from the Bay every year. A decontamination project started in 1982 dramatically decreased the flow of mercury from the Bay to the Sea. A historic rainfall in 1982 also "purified" the surface sediments. Organic mercury concentration in the sea water was 5.1 ng/l while total mercury was 120 ng/l at the center of the Bay in 1985.

Mercury concentrations in bed sediments of the Yatsushiro Sea outside Minamata Bay were observed at 24 sampling locations during 1975 and consecutive years. The majority of the bed sediments contains less than 1 ppm of mercury and the degree of mercury contamination dispersed outside the Bay is not yet serious. However, mercury movement from Minamata Bay, within which bed sediment mercury concentration is as high as 300 ppm, into the surrounding area of the Yatsushiro Sea has rapidly accelerated during the past few years. During the 15 years from 1960 and 1975, roughly 9 tons of mercury moved from the Bay, while almost 17 tons moved out between 1975 and 1978. Increase of methyl- mercury in bed sediments at the sea was 0.10 tons from 0.56 tons in 1975 to 0.66 tons in 1978 or 5.8% increase per year, while total mercury in bed sediments at the Sea increased at a rate of 42% per year. Future movement of mercury in these sediments appears to be predictable and may serve as a model for the migration of other contaminated bed sediments.

A description is given of five cases of methyl mecury poisoning observed at a factory for the manufacture of such compounds, in a seed-dressing plant and a saw-mill. The cases show a striking resemblance to seven others previously described in the literature. An account is given of the steps, both technical and medical, that have been taken to protect the staff from the risks of poisoning. Particular attention must be paid to repeated environmental and medical examinations, including both blood and urine tests for mercury frequently repeated during the period of exposure.

Papers presented at the International Congress of Scientists on the Human Environment, Kyoto, Japan, 1975, relating to observations of Japanese scientists on the Canadian mercury pollution situation, have been summarized and are discussed.

Japanese legislation relating to mercury discharges is reviewed, as well as compensation law, clean-up procedures, and financial assistance provided to chlor-alkali plants converting from mercury to diaphragm cells.

Several industrial installations were visited, and the mercury control measures and technology at two Japanese chlor-alkali plants are discussed in some detail.

The physiology and ecology of mercury-resistant, mercury-metabolizing bacteria from Chesapeake Bay were studied over a three year period. Six stations, representing various levels of environmental quality were monitored, permitting analysis of the seasonal occurrence and abundance of microorganisms resistant to an array of inorganic and organic mercury compounds and heavy metal ions. Evidence was obtained which estalishes a role for bacteria in the cycling of mercury in the estuarine environment. The role of bacteria in the movement of a simplified food chain, i.e., concentration of mercury in oyster tissue via bacterial action, was established. The route of mercury in an aquatic food chain at the bacterial- protozoan level has also been investigated. Studies showed 230 Hg-labeled bacteria, a Pseudomonas sp., are taken up by a bactiverous ciliate, Keronopsis pulchra, with a resultant increase in mercury concentration in the ciliate. The data accumulated to date indicate that bacteria play and important role in the amplification of mercury in aquatic food chains.

Mercury body burdens of aquatic organisms are contributed to by mercury uptake from the ambient water and mercury uptake from the food. To assess the relative importance of each route, we conducted a series of laboratory experiments with the natural foodchain Daphnia pulex (water flea) and Gambusia affinis (mosquito fish). The organisms were tagged with radioactive (203 Hg) methylmercury amended to their water and food. Uptake tests were run at 0.2, 0.1 and 0.05 ng/ml. Uptake rates, assimilation efficiency, and elimination rates for the fish and uptake and elimination rates for Daphnia were determined for methylmercury. A simple model was developed to clarify methylmercury transfer. Daphnia pulex acquired methylmercury from ambient water much faster than Gambusia, but uptake rate was not linear with respect to water methylmercury concentration. Daphnia eliminated methylmercury at a biological halflife (Tb) of 3.2 days. Gambusia assimilated methylmercury from water and foodat similar rates, but did not show a detectable elimination rate. Food was shown to be a significant source of methylmercury in Gambusia, but not in Daphnia.

Mercury transfer from bed sediments to fresh wa ter fish was observed for 20 days in the laboratory. Organic-rich sediments from the Ottawa River were contaminated with mercuric chloride to produce a total mercury concentration of 1.023 ppm.

Two possible mercury routes from bed sediments to fish were quantitatively evaluated. The concentration of mercury accumulated in fish from bed sediments was nine times higher than that accumulated from water in which mercury had come from bed sediments. The mercury concentration in individual fish varied considerably.

Suspended sediments (solids) contribute 58% (982 kg per year of all mercury transported downstream in the study section of the Ottawa River. Although filtered water contains a low mercury concentration (13 ng/l or 0.013 ppb), it accounts for 41% (689 kg per year) of all mercury transported downstream. The role of bed sediment movements on the mercury transport is very small, only 1%, in the study section. Most of the mercury (96.7% of total mercury and 97.8% of methylmercury) is in bed sediments. Biomass contains an insignificant portion of mercury (0.2% of total mercury and 1.7% of methylmercury), though it has a higher ratio of methylmercury to total mercury; plants (20%), invertebrates (40%) and fish (85%). Methylmercury production and destruction are in equilibrium in water and sediments without biological agents, such as higher aquatic plants, invertebrate and fish.

1. The enzymes leading to the methylation of homocysteine have been examined in three micro-organisms: a cobalamin-producing bacterium, Bacillus megaterium; a yeast, Candida utilis; and a basidiomycete fungus, Coprinus lagopus. The yeast and the fungus contain negligible endogenous cobalamin.
2. Extracts of cach organism catalyse C1- transfer from serine to homocysteine with a polyglutamate folate coenzyme.
3. The enzymes generating the methyl group of methionine from C-3 of serine have similar properties in each case, but different mechanisms of homocysteine transmethylation from 5-methyltetrahydrofolates were found.
4. B. Megaterium contains an enzyme with properties suggestive of a vitamin B12-dependent homocysteine transmethylase, whereas Cand. utilis and Cop. Lagopus transfer the methyl group by a reaction characteristic of the cobalamin-independent mechanism established for Escherichia coli.
5. The specificity of each transmethylase for a 5-methyltetrahydropteroylpolyglutamate is consistent with the results of analyses of endogenous folates in these organisms, which showed only conjugated forms.
6. None of the extracts catalysed methionine production from S-adenosylmethionine and homocysteine.
7. These results are compared with results now available for methionine synthesis in other organisms, which show a considerable diversity of mechanisms.

About 15 kg of plutonium was used in the Nagasaki A-bomb, but only 1 kg was fissioned and the rest (14 kg) was released into the environment. The fate of this plutonium was investigated at the east side of Nagasaki city where the local fallout was deposited. The four objectives investigated concerning the unfissioned 239+240 Pu were:

1. the geographical distribution up to 100 km from the hypocentre,
2. the vertical movement of the deposited plutonium within a soil core and a reservoir sediment core,
3. the ecological distribution, and
4. an estimation of the total mass deposited as local fallout.

The highest concentration of 230+240 Pu, 64.5 mBq/g, was found at a point 2.8 km from the hypocentre. The local fallout was observed over a limited area up to 18 km east from the hypocentre. Plutonium was mobile within the soils and reservoir sediments. For the former an amount of 10% moved downward during the last four decades and the rest (90%) remained within 10 cm from the surface. A considerable amount of plutonium was found in fish (0.0195 mBq/g dry), freshwater shellfish (0.0278 mBq/g dry), ginger root (0.0366 mBq/g dry), and sweet potato (0.0110 mBq/g dry). An estimation of plutonium deposited as local fallout from the A-bomb was 37.54 grams.

Our discovery that metal-alkyls are synthesized in the environment by a reaction involving electrophilic attack on the cobalt-carbon bond of methyl-B12 prompted us to look in some detail at the biochemistry of organometallic and coordination complexes of toxic metals. We have discovered metabolic cycles for mercury, tin, selenium and arsenic. Vitamin B12 plays a central role in the biosynthesis of organometallic compounds in biology. The kinetics and mechanism for the biosynthesis of methylmercury, dirnethylmercury, methylmercury thiomethyl and phenylmethylmercury will be discussed in the context of electrophilic attack on the cobalt-carbon bond of methyl-B12. Similar reactions have been demonstrated for the synthesis of dimethyl and trimethyl-tin, methyl and dimethyl palladium and dirnethyl gold.

Recently we discovered that the synthesis of monomethyl-tin occurs by oxidation-addition to methyl-B12. In this reaction stannous ion reacts with methyl-B12 (CoIII) to give methyl-stannic ion and reduced B12 (CoI). The discovery of this new reaction mechanism for methylation of metals suggests that oxidation-reduction couples may occur for a number of toxic metals (e.g. SnII and SnIV, TII and TIIII, AsIII and A5V, or As-III and As-I, or AsI and AsIII, SeIV and SeVI, PbII and PbIV, etc.). The reaction with arsenic is particularly pertinent because the mechanism for the biosynthesis of dimethyl and trimethylarsine remains a controversial issue, although rnethyl-B12 has been implicated as the methyl-donor for biomethylation of this element.

The biomethylation of metal ions in the sea deserves special consideration, because it has been shown that methyl iodide is synthesized biologically in the marine environment. One mechanism for the biosynthesis of methyl iodide involves electrophilic attack on the cobalt-carbon bond of methyl-B12 by molecular iodine. Moleculariodine is known to be a naturally occuring molecule in the sea, because it is synthesized by kelp. Marine bacteria, especially Pseudomonas species, are known to be involved in the biosynthesis of B12. Methyl iodide is capable of alkylating a number of metal ions, and so it is anticipated that facile methyl-transfer reactions between metal alkyls (i.e. disproportionation reactions) may be very important in the marine environment. This would explain why methyl-mercury bioaccumulates at a naturally high level in tuna fish and sword fish.

Antifoulants containing organotins such as tributyltin (TBT) have been widely used throughout the world because of their effectiveness in inhibiting marine growth and barnacles on boat hulls, to reduce drag and fuel consumption.

However, research has demonstrated many adverse effects of the highly toxic organotins on marine life, including economically important species such as oysters. These include acute toxicity through bioconcentration and bioaccumulation in shellfish and fish, reduced growth rates and shell thickening in shellfish, for example. Grave concern has been expressed over the high levels of organotins found to be accumulating in New Zealand marinas. It is also possible that organotins may have an adverse effect on human health. The problem is complicated by the fact that the levels of toxicity of organotin occur at the limits of chemical detection.

A need was identified for Government action to address the problem in New Zealand. The Minister for the Environment, following a request from the Parliamentary Commissioner for the Environment, directed the Ministry for the Environment to convene a working party to investigate and report to him as soon as possible. The terms of reference were to determine the extent to which restrictions on the use or availability of organotin antifoulants are necessary and the ways in which such measures can be effectively implemented. The Working Party terms of reference were restricted to consideration of the use of organotins as antifoulants, and not other uses such as in timber treatment and as a biocide in air conditioning systems. It should be noted that the economic implications of the different management options have not been accurately assessed.

The working party investigation included a consultative process involving the circulation of draft reports to interested agencies and individuals, andthe convening of meetings to discuss the draft report and submissions received from interested parties.

At its first meeting the working party extended its terms of reference to include antifoulants that contain organotins and not just tributyltins (TBT). The working party was of the opinion that if recommendations limiting the use of TBT antifoulants were considered necessary, it would be of concern if subsequent regulations could not be applied to the use of compounds in antifoulants that were very similar chemically and which behaved similarly within the environment.

At the working party's December 1987 meeting (at which the NZ Paint Manufacturers Association representative was absent), there was unanimous agreement to the following recommendations, which were included in an interim report sent to theMinister:

• That the working party favours a complete ban on the manufacture, importation, supply, sale and use of all antifoulants containing organotins;
• That the working party expresses concern over other uses of organotins. such as for timber treatment and in air conditioning systems, and requests that further study be made of this issue.

After the December 1987 meeting, the positions of some members of the working party changed. In addition, the views of a number of other interested agencies and individuals were taken into account. There was still unanimous agreement amongst members that a problem existed in the continued use of antifoulants containing organotins, but there were a variety of views as to the extent of the problem, and how best to manage it. Consequently, the working party recommendations to Government have been presented in the form of three future management options aimed at alleviating the problems associated with the use of organotin antifoulants. The working party report also identifies who supports particular options, and the implications of each option. These options include a total ban which could be introduced to take effect immediately or progressively over a number of years, and a progressive partial ban.

The report is now forwarded to the Minister for the Environment for Government action and policy decision.

The Pesticides Board, in their draft 1987/88 annual report. have agreed that they will take into account any recommendations arising out of the report of the working party, when considering the registration of organotin compounds.

The options and associated recommendations are summarised below, together with an indication of who supports them.

An Immediate Total Ban wou]d apply to all antifouling formulations containing organotin, and to all vessels.

The Progressive Total Ban would involve a two-stage ban: all organotin antifoulants would be banned with the exception that for a two year transition period only, slow-release copolymer organotin antifoulants could be used under controlled conditions on vessels greater than 25 metres.

The Progressive Total Ban is not supported as a first choice by any of the working party members, but is supported as a second choice by the Auckland Harbour Board and is also favoured by a number of other agencies and individuals.

The Progressive Partial Ban is similar to the Progressive Total Ban, but with exemptions for alurninium hulled vessels and outdrives, and that after a two year transition period, the continued use of copolymer organotin antifoulants be subject to review of the extent of the problem and availability of proven alternative antifoulants.

This research was designed to address a number of criticisms of imposex studies. Variability in imposex intensity between populations was found to be the result of an enviromental effect, in particular variation in TBT concentrations in the water, rather than the result of genetic variability between populations. Genetically different populations of N. Canaliculata from Alaska, Cape Beale and Wizard Island, showed similar imposex intensities when exposed to the same flow through water system at Bamfield Marine Station.

Average female penis lengths did not differ significantly in live, frozen and specimens preserved in 4% formalin. Average male penis length of frozen specimens however, differed significantly from live and specimens preserved in 4% formalin. Results suggest the possibility of differential penis preservation in males and females. Different observers had no significant effect on imposex measurements and data of different observers may be compared with confidence.

Temporal analysis of imposex in N. Canaliculata at the Victoria Harbour breakwater, showed that imposex intensity was significantly greater in the summer months than in the fall. Male penis length varied little in this population.

The expression of imposex in female N. canaliculata, N. emarginata and Searlisia dira has been shown to be a good indicator of TBT contamination in a given location but the RPS index of imposex intensity should be used with care so as not to lead to erroneous conclusions in data interpretation.

This report provides a summary of information on organotin compounds in the British Columbia environment obtained as a result of studies conducted by Environment Canada Pacific and Yukon Region between 1984 and 1995. These studies were conducted to determine the presence of organotin compounds near known or suspected sources of release to the coastal environment of British Columbia. Although the studies focused primarily on butyltin compounds, limited information on cyclohexyltin and phenyltin compounds was also obtained.

The objective of this report was to document existing information on organotin compounds in British Columbia with respect to levels in the environment; past and present uses; current legislation and guidelines controlling the use and release of these compounds; and, where possible, the efficacy of these measures in reducing releases and improving environmental quality.

A general overview of toxicity and environmental levels of these compounds in other areas of Canada and the world has been provided to allow the reader to put the data for British Columbia into perspective.

Following observations of growth abnormalties in oysters, Crassotrea gigas, from Nanoose Bay, samples of sediments, water and oyster tissue were analysed for organotins. Highest concentrations of tributyltin (TBT) in both sediments and water were measured at a salmon farm, and highest concentration of TBT in oysters was measured at an oyster farm adjacent to the salmon farm. In March, 1987, Environment Canada and Agriculture Canada advised the aquaculture industry that TBT is not permitted for use as a marine growth retardant on net pens and the products are no longer available in retail outlets.

The Workshop on Organotin Compounds in the Canadian Aquatic Environment was held at the Institute of Ocean Sciences, Sidney, British Columbia, on February 19-20, 1996. This was the first Canadian workshop on organotin compounds. Its purpose was to bring together all researchers, managers of fisheries resources, regulators, and other interested parties to discuss, primarily, the Canadian situation with respect to the extremely toxic antifouling agent tributyltin (TBT), and to a lesser extent, other pesticidal and non-pesticidal organotin compounds. These proceedings summarize formal presentations and discussions on (i) the history of TBT research and monitoring in Canada, (ii) what effect the regulation of antifouling uses of TBT under the Pest Control Products Act in 1989 has had on concentrations of TBT in water, sediment and aquatic biota in Canada, (iii) the present status of non-pesticidal organotin compounds in Canada under the Canadian Environmental Protection Act, (iii) recent advances in analytical methods, biological chemistry and environmental pathways of organotin compounds, (iv) the leaching of organotin compounds from chlorinated poly(vinyl chloride) pipe into drinking water, and (v) bioaccumulation, biomonitoring and the toxicity of organotin compounds to aquatic biota. It was concluded that the 1989 TBT regulation has not been effective in reducing TBT levels at many locations to below toxicity endpoints or Canadian Water Quality Guidelines for the protection of aquatic life. These proceedings make recommendations for further action in the areas of regulation, research and monitoring. These proceedings also include the workshop program, abstracts of the presentations, addresses of the participants, their current and planned activities on organotin compounds, a list of their publications, and the addresses of those few other organotin researchers (and managers) in Canada who did not attend the workshop.

Non-pesticidal organotin compounds (notably mono- and di- methyltin, butyltin, and octyltin compounds) are not manufactured in Canada. They are imported, however, mainly for use as poly(vinyl chloride) (PVC) stabilizers and are also used as industrial catalysts. Data identified for 1984 indicate that approximately 290 tonnes of methyltin compounds, 1020 tonnes of butyltin compounds, and a much smaller quantity of octyltin compounds were imported to Canada. More recent data have not been identified.

Based on limited fate information, non-pesticidal organotin compounds are expected to exist predominantly in the aquatic environment. The mono- and di- alkyltin compounds are water-soluble and are not expected to volatilize from water in significant quantities. They undergo biodegradation and photolysis in water and are not expected to persist for long periods. Mono- and di- methyltin and mono- and di- butyltin have been detected in water and sediment at several locations in Canada. However, the sources of these compounds to the environment are uncertain. The methyltin compounds may have resulted from the natural methylation of tin or from anthropogenic sources. The butyltin compounds were primarily degradation products of the pesticide tributyltin, the antifouling use of which has been regulated in Canada since 1989. Leaching of organotin-stabilized PVC pipe by water could also be a source of organotin entry into the Canadian environment.

The assessment of effects on the environment focused on aquatic biota since they are the most likely to be exposed to non-pesticidal organotin compounds. There is limited information on the toxicity of most of these compounds to organisms in both the freshwater and marine environments. Nonetheless, it was possible to compare estimated effects thresholds to nvironmental concentrations for the mono- and di- methyltin and mono- and di- butyltin compounds. None of the effects thresholds was exceeded by environmental concentrations found in areas where contamination was suspected, indicating that these compounds are unlikely to cause harmful effects to freshwater or marine biota in Canada. Exposure to mono- and dioctyltin compounds is unlikely since they have not been found in Canada or elsewhere in any environmental medium. Although toxicity data for the octyltin compounds are lacking, it is unlikely that they would cause harmful effects to aquatic biota.

The non-pesticidal organotin compounds that were assessed are not volatile and are not expected to contribute to phenomena such as ozone depletion, global warming, or the formation of ground-level ozone.

Available data are insufficient to serve as a basis for estimation of the exposure of the general population to any of the non-pesticidal organotin compounds. Available data on the toxicity of these compounds in experimental animals and humans are also limited.

Based on these considerations, the Minister of the Environment and the Minister of National Health and Welfare have concluded that non-pesticidal organotin compounds do not constitute a danger in Canada to the environment or to the environment on which human life depends. Therefore, non-pesticidal organotin compounds are not considered to be "toxic" as defined under Paragraphs 11(a) and 11(b) of the Canadian Environmental Protection Act (CEPA). However, the Ministers have concluded that it is not possible to assess whether any of the non-pesticidal organotin compounds constitutes a danger in Canada to human life or health as defined under Paragraph 11(c) of CEPA.

Tropical species of Nassarius (family Nassariidae, order Neogastropoda) have been described taxonomically but have not been investigated ecologically in any detail. The temperate species have fared much better in terms of number of studies and diversity of subjects covered, for which a brief review is presented.

The five species observed in this study, N. pullus, N. luridus, N. coronatus, N. dorsatus and N. albescens were examined for seaward pattems in distribution over a mudflat, Cockle Bay (Magnetic Island) for the period October, 1988 and May, 1989. It was observed that each species was not sampled over the entire Site but found in "zones" which did overlap to some degree. The inshore sites, 40 metres and less had two species present N.dorsatus and N. pullus. Stations at 60 metres and 80 metres were found to have three species present N. pullus, N. luridus and N. coronatus. Stations located at 100 metres seaward only had N. luridus and N. pullus. These zones were maintained for most species over the sampling period with the exception of N. turidus which appeared to be more confined to the seawards stations in the later months of sampling. A number of explanations are suggested to explain these observations such as interspecific competition and different physiological tolerances in the species. There is no conclusive evidence for either of these factors to account for this pattem.

An investigation of imposex, the expression of male characters in females, was initiated in this study. The documentation of this feature in other species of Nassarius and neogastropods has been reviewed, including the relationship between imposex and Tributyltin (TBT- a marine antifoulant in protective marine paints). It was noted that imposex did occur in the spcies examined, N. pullus, N. luridus, N. dorsatus, and N. coronatus, and that the ratio of imposex individuals within a sample changes between sites. The highest levels of imposex were recorded for the reclaim site for N.pullus (90.43 %) and N. dorsatus, Pallarenda (78.57%). There were no cases of imposex recorded at Cockle Bay for N. dorsatus and N. coronatus. The implications of these results in relation to TBT are discussed in addition to the role of monitoring TBT in the Great Barrier Reef Marine Park.

Four species of Nucella occur in the BC/ Alaskan region: N. lamellosa, N. emarginata, N. canaliculata and N. lima. Recent generic usage is to accept Nucella as separate from Thais, and not a sub-genus. Where N. lima and N. emarginata have reduced spiral ridges so that shells are almost featureless, it may not be possible to identify specimens to species based on shell morphology. N. emarginata is the species most likely to be found near high tide and on exposed shores. N. lamellosa is most likely to be found nearest low tide on sheltered shores. N. canaliculata is intermediate. N. lima may replace N. lamellosa towards Alaska.

A simple 3-step dichotomous key for the four species was developed based on siphonal canal length, whorl separation and spiral ridges. A computerised taxonomic database (DELTA) provided concise natural language descriptions of the species based on a character/species matrix developed, but could not generate a satisfactory key due to the overlap in characters between N. lima and N. emarginata.

1. The distribution of Neogastropods (Gastropoda: Prosobanchia) was studied for the Indo-Pacific area, and two checklists were elaborated: one including all genera found in the Indo-Pacific and the other for intertidal species within the Thaisidae family.
2. A preliminary identification key for the intertidal genera Thais and Mancinella was generated using the australian program DELTA.

The pseudohermaphroditism of the Prosobranch Nucella lapillus is described, basing on detailed anatomical and histological investigations (compare tab. 1). In addition to the dominant female determinated pseudohermaphroditism (the fertile female organs are supplemented by a penis (fig. 1 f)) also the rare male determinated case is represented, where instead of male parts of the reproductive system the corresponding female parts are obvious (fig. 1 g).