Acute and chronic toxicities of tributyltin to various life stages of the marine polychaete Hydroides elegans

Experiments were performed to determine the acute and chronic toxicities of tributyltin (TBT) (nominal concentrations) to polychaete Hydroides elegans. Firstly, static tests were performed to examine the lethal effect of TBT on five life stages of H. elegans. The 48-h LC(50) (95% CI) for the eggs, 2-cells, trochophores, juveniles and adults was 0.18 (0.15-0.20), 0.97 (0.77-1.23), 2.36 (2.11-2.65), 2.86 (2.63-3.12) and 4.36 (4.04-4.71) microg TBT l(-1), respectively. Secondly, a 17-d static renewal chronic test was conducted to study sensitivity of the early development (egg to juvenile) to TBT. The survivorship, percent settlement and time to reach settlement were significantly reduced at 0.01 microg TBT l(-1). Effects of TBT on the juvenile growth and maturation were also studied through a 44-d chronic test. Lower survivorship and reduced tube growth were observed only at >or= 1 microg TBT l(-1), however, only H. elegans exposed to or= 0.1 microg TBT l(-1). Our results indicate that the early development of H. elegans is highly sensitive to TBT and this polychaete can be routinely employed as a test organism for both acute and chronic ecotoxicity bioassays in tropical and subtropical regions such as southern China.     

Determination of butyltins in harbour sediment and water by aqueous phase ethylation GC-ICP-MS and hydride generation GC-AAS

Sediment and water samples have been collected between 1992 and 1995 for evaluating butyltin contamination in two marinas from the coastal area in The Netherlands, two years after the ban of TBT. Sediments extracts were analysed by capillary gas chromatography-inductively coupled plasma-mass spectrometry. Sediment concentrations for TBT showed no trend of decrease between 1992 and 1995 and were extremely high in the marina secluded from tidal action; 17.5 +/- 8.0 microg g(-1) and much lower for the marina with tidal action; 0.117 +/- 0.073 microg g(-1). High ratios between TBT and DBT in the sediments indicate that degradation mechanisms in the sediments are of minor importance. Dissolved butyltin compounds were analysed in water by means of gas chromatography-atomic absorption spectrometry. Water concentrations of TBT showed no clear trend of decrease between 1992 and 1995 and were high in the marina secluded from tidal action; 139 +/- 166 ng litre(-1) but much lower for the marina with tidal action; 48 +/- 98 ng litre(-1). An active degradation mechanism during summer periods was indicated by low (<1) TBT/DBT ratios in the water phase of the marina secluded from tidal action.     

Concentrations of organotin compounds in sediment and clams collected from coastal areas in Vietnam

Levels of butyltin (BT) and phenyltin (PT) compounds were determined in sediments and clam Meretrix spp. collected from north and central coastal areas in Vietnam. Concentrations of TBT in sediments ranged from 0.89 to 34 ng g(-1) dry wt and those in clams ranged from 1.4 to 56 ng g(-1) wet wt. The levels of TBT in sediments and clams from Vietnam were within limits reported from other countries. Further, the TBT level in clams was lower than the tolerable average residue level (TARL) estimated based on tolerable daily intake (TDI). Trace amounts of PTs were also found in both sediment and clam samples. In sediments from north and central Vietnam, the concentrations of TBT were highest in the order of Hue (28 ng g(-1) dry wt), Cua Luc (15 ng g(-1) dry wt), Sam Son (6.3 ng g(-1) dry wt), and Tra Co (5.5 ng g(-1) dry wt). Among the clams from north and central Vietnam, the levels of TBT in clams from Cua Luc were dramatically high at 47 ng g(-1) wet wt. TBT formed the principal butyltin species in sediment at all sites studied. The ratios of TBT in sediment were higher among BT compounds at all study sites. Of total BTs, TBT was the dominant species in clams from almost all sites studied. In spatial distribution, TPT showed a pattern similar to TBT, suggesting the use of TPT as an antifouling paint. The partition coefficient between sediment and calms was calculated. The partition coefficients of TBT and TPT were 2.01 (0.56-5.5) and 9.23 (3.1-20), respectively. These results show that sediment-bound TBT is a source of contamination to clams in addition to dissolved TBT.     

Short-term effects of metals on the filtration rate of the zebra mussel Dreissena polymorpha

In order to study the short-term ecotoxicity of metals to the freshwater mussel Dreissena polymorpha, the effects of Cu, Zn and Cd on the filtration rate of this mussel were determined in laboratory experiments. Filtration rate was chosen as the endpoint, because it is a sensitive sublethal parameter compared to mortality and it is an important parameter given the ecological role D. polymorpha fulfills. The filtration rate was calculated from the decrease in algal concentration, fed to mussels in aquaria, containing different metal concentrations. The EC50 for Cu (41 microg litre(-1)) was lower than for Cd (388 microg litre(-1)) and Zn (1350 microg litre(-1)). The NOEC(accumulation) for the essential metal Zn was higher than for the essential metal Cu. Cadmium, a non-essential metal, was accumulated at all elevated water concentrations, so the NOEC(accumulation) was the concentration in the control water (<0.2 microg litre(-1)). All (no) effect concentrations found in this study were above the quality criteria set for metal concentrations in Dutch surface water, suggesting that the zebra mussel is sufficiently protected by these quality criteria.     

Effects of the parasiticide ivermectin on the cladoceran Daphnia magna and the green alga Pseudokirchneriella subcapitata

Although widely used for the treatment of endo- and ectoparasites in livestock and pets, very few data on chronic effects on aquatic organisms are available for the parasiticide ivermectin. In the present study, toxicity of ivermectin to two freshwater organisms, the cladoceran Daphnia magna and the green alga Pseudokirchneriella subcapitata was investigated. For D. magna, a mean LC(50) 48 h of 5.7 ngl(-1) was derived from 10 acute tests. Chronic toxicity of ivermectin to D. magna was extremely high: with 0.001 and 0.0003 ngl(-1), respectively, nominal LOEC and NOEC based on growth and reproduction were far below the analytical limit of detection for this compound. P. subcapitata was considerably less sensitive to ivermectin than D. magna. For both growth rate and yield, EC(50) was >4,000 microgl(-1), LOEC was 1,250 microgl(-1) and NOEC 391microgl(-1). In view of the high toxicity to D. magna, the use of ivermectin might pose a risk to local aquatic ecosystems. Further studies should be carried out to investigate the effects of ivermectin and its degradation products on pelagic and benthic freshwater invertebrates.     

Chronic effects of vapour phase di-n-butyl phthalate (DBP) on six plant species

A fumigation experiment was performed in which six plant species representing the European flora were exposed to a range of DBP concentrations. Controlled amounts of DBP-saturated air were injected into the ingoing air-streams of plant fumigation chambers, maintaining constant concentrations there for a period of up to 76 days. The target concentrations were a control, 0.8, 1.5, 3.5, and 10.0 microg m(-3). The variation in sensitivity between plant species to atmospheric DBP was quantified on the basis of whole plant biomass in order to derive no-observed-effect-concentrations (NOECs). Significant dose-response relationships, based on realised concentrations, were thus derived using non-linear regression, resulting in NOECs of 0.51 microg m(-3) for Trifolium repens, 0.96 microg m(-3) for Brassica campestris, 1.87 microg m(-3) for Phaseolus vulgaris and 2.21 microg m(-3) for Plantago major. A significant effect was also observed for Holcus lanatus at 12.4 microg m(-3) DBP, but due to the variation at lower levels of DBP exposure, no dose-response relationship could be derived. No significant effect on growth of current year needles in Picea abies was observed, even at the highest level of DBP, 13.7 microg m(-3). Based on statistical extrapolation according to Aldenberg and Slob [Ecotox. Environ. Safety, 25 (1993) 48], an overall predicted no-effect concentration (PNEC) for the plant-atmosphere compartment of 0.33 microg m(-3) DBP was calculated. The PNEC was calculated using the mean and standard deviation of the NOEC for four of the tested species and an extrapolation factor. In addition to changes in leaf colour, leaf crinkling and growth reduction, a number of not quantified observations are described, indicating that DBP affects the physiology as well as the morphology of these species.     

Effect of TBT on Ruditapes decussatus juveniles

The effects of sublethal concentrations of tributyltin (TBT) on growth of juvenile clams Ruditapes decussatus were determined during exposure to TBT concentrations of 50, 100 and 250 ng l(-1) (as Sn) for a period up to two years. Length and weight of clams increased continuously in all treatments throughout the experimental period, and, overall, rates were not significantly influenced by TBT exposure, although final length and weight were inversely related to increasing TBT concentration. Juvenile R. decussatus therefore appear to be less sensitive to TBT than larval stages. Some juveniles exposed to TBT developed abnormal shell growth, laterally, changing the typical flattened shape of clams into a more "rounded" form. This characteristic was more visible in the anterior margins of valves than posteriorly, and mainly observed in clams exposed to TBT at 50 ng l(-1) (as Sn).     

Organotin concentrations in three intertidal neogastropods from the coastal waters of Taiwan

This study was aimed to determine organotin concentrations in the muricids Thais clavigera, Thais tuberosa and Morula granulata on an island wide scale and to find an adequate bioindicator species for long-term monitoring purpose. Samples were collected from the coast of Taiwan and vicinity islands with organotin analysis by graphite furnace atomic absorption spectrophotometry. Because triphenyltin (TPT) could not be discriminated from tributyltin (TBT) by the extraction method, organotins were measured as TBT + TPT and total hexane extractable organotins. Severity of imposex in the muricid population samples expressed as relative penis size (RPS) indices were calculated and compared to determine a suitable bioindicator species. In T. clavigera, T. tuberosa and M. granulata, TBT + TPT were 17-157, 1-44 and 117-1343 ng Sn g(-1) dry wt, respectively. And total organotins varied in the range of 181 to 1125, 23 to 44 and 229 to 1402 ng Sn g(-1) dry wt, respectively. A positive correlation was found between TBT + TPT and total organotins in M. granulata (TBT + TPT = Total organotins x 1.01-110.79; R2=0.97; p<0.001). At the site of Dapaisha, total organotins in M. granulata was 10 times higher than in T. tuberosa (i.e. 242 versus 23 ng Sn g(-1) dry wt). No signs of imposex were found in T. tuberosa (a single site in two subsequent years) and in M. granulata (seven collection sites). The degree of imposex (RPS) of T. clavigera varied from 0.2 to 38.1%. The RPS indices from fishing harbors were not higher than from rocky shores and oyster culture sites. No correlation was found between RPS indices and concentrations of TBT + TPT or total organotins. M. granulata seemed to be insensitive to organotin pollution although organotins were also detected. Our results indicate that organotin pollution is wide spread in coastal waters of Taiwan and pollutants at least include butyltins and phenyltins. As a bioindicator species, T. clavigera is more appropriate than T. tuberosa and M. granulata to monitor organotin contamination.     

Butyltin compounds in sediment and molluscs from the shipping strait between Denmark and Sweden

The distribution of tributyltin (TBT) contamination in the subtidal zone of the waters between Denmark and Sweden was investigated in relation to major international shipping lanes. Sediment and different benthic molluscs were sampled in transects along and perpendicularly to the shipping lanes in the Sound (?resund) and the Kattegat/Skagerrak region. The samples were analysed for TBT and its degradation products, dibutyltin (DBT) and monobutyltin (MBT), using GC-PFPD. In sediments, the TBT concentration ranged from <1 to 19 ng g(-1) dry weight (dw) with a strong correlation between the TBT concentration and the organic fraction in sediment (r(2)=0.90) in the samples collected in the Sound, where the highest concentrations were found. This relationship was not observed in the samples from the Kattegat because the TBT concentration in most sediment samples was below the limit of detection. In the molluscs, TBT and its degradation products were detected in all samples from the entire area with concentrations ranging from 8.1 ng g(-1) dw in Buccinum undatum to 1316 ng g(-1) dw in Nuculana pernula. The deposit-feeding bivalve N. pernula was found to have a particularly high accumulation potential for TBT. In addition, a strong correlation between TBT concentrations in sediment and N. pernula was found. Therefore this species seems to be an ideal organism for monitoring sediment contamination. The TBT concentration in N. pernula was found to decrease gradually along the shipping lanes from the Sound, through the Kattegat and into the Skagerrak.     

Tributyltin in environmental samples from the Former Derecktor Shipyard, Coddington Cove, Newport RI

Tributyltin (TBT) was detected in all 24 surface sediment (top 2 cm) samples collected from Coddington Cove, Newport, RI. TBT surface sediment concentrations ranged from 32 to 372 ng Sn/g with a mean concentration of 146 ng Sn/g. Analyses of selected core sections detected TBT in at least the top 18 cm at all 7 stations where cores were collected. No consistent TBT concentration trends with depth for these cores suggest mixing is an important process in the sediment column. In one core (station 28), TBT was found in the 76-86 cm section at a concentration of 141 ng Sn/g; thus sediments are a significant sink for TBT. However, sediment mixing processes can enhance releases of bioavailable TBT. Mussels, clams and fish from Coddington Cove contain TBT at concentrations ranging from 9.2 to 977 ng Sn/g. TBT concentrations in lobsters were below the detection limit (<6 ng Sn/g). Based on available screening criteria, TBT concentrations in Coddington Cove sediment is likely to be having an adverse effect on the biota at some locations.     

Distribution of organochlorine pesticides and heavy metal residues in fish and shellfish from Calicut region, Kerala, India

Fish collected from five different locations from the Calicut region, India were analysed for the levels of organochlorine pesticides (OCPs) and heavy metal (HM) residues in order to elucidate the status of these chemical contaminants in fish and shellfish meant for human consumption. The highest concentrations of OCPs detected in the edible portion of fish were 10.47, 70.57 and 28.35 ng g-1 wet weight, in marine, brackish water and freshwater, respectively. BHC and heptachlor epoxide formed the major share of OCPs in the marine fish while BHCs contributed to the major share in the freshwater and brackish water fish. The DDT (sum of DDT and its metabolites) ranged from 0.05 to 8 ng g-1 in the samples irrespective of the habitat. Among the HMs, Cu, Zn, Mn and Cr were present in the samples irrespective of the place of collection. About 22% of the samples from the freshwater area contained marginally higher lead content above the legal limit of 0.2-0.4 microg g-1. The Cr content ranged from 0.1 to 1.1 microg g-1 in the fish with marginally higher content in the fish from freshwater and marine regions (0.55-1.1 microg g-1). Mercury was detected in the samples (55%) from marine habitat only. The concentrations of OCPs and HMs in the samples, in general, were below the maximum residual level recommended by various organizations.     

Aquatic toxicity of cartap and cypermethrin to different life stages of Daphnia magna and Oryzias latipes

Cartap and cypermethrin, which are among the most widely used pesticides in many countries, are considered safe because of their low mammalian toxicity and their low persistence in the environment. However, recent findings of endocrine-disrupting effects and developmental neurotoxicity have raised concerns about the potential ecological impacts of these pesticides. We evaluated the aquatic toxicity of cartap [S,S'-(2-dimethylaminotrimethylene) bis(thiocarbamate), unspecified hydrochloride] and cypermethrin [(RS)-alpha-cyano-3-phenoxybenzyl-(1RS,3RS,1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate], both individually and combined, on different life stages of the freshwater cladoceran Daphnia magna and a freshwater teleost, Japanese medaka (Oryzias latipes). The 96-hr Daphnia median effective concentrations (EC50s) for cartap and cypermethrin were 91.0 microg/L and 0.00061 microg/L, respectively. Rapid recovery of Daphnia was observed after short-term pulsed exposure to cartap and cypermethrin; there were no adverse effects on reproduction or survival 20 d after a 24 hr exposure to cartap up to 1240 microg/L and cypermethrin up to 1.9 microg/L. Chronic continuous exposure (for 21 d) of 7-d-old Daphnia to cypermethrin significantly reduced the intrinsic population growth rate in a concentration-dependent manner. However, because the intrinsic population growth rates were all above zero, populations did not decrease even at the highest experimental concentration of 200 ng/L. Exposure of Daphnia neonates (< 24 hr old) to cypermethrin for 21 d caused significant, sub-lethal reproduction-related problems, such as increased time to first brood, reduced brood size, and reduced total brood number, at 0.0002, 0.002, and 0.2 ng/L cypermethrin, but the intrinsic population growth rate was not significantly affected. Oryzias latipes was relatively more resistant to both pesticides. In particular, embryos appeared to be more resistant than juveniles or adults, which may be partly due to the protective role of the chorion. The incidence of larval fish deformity was significantly higher after a 96 hr exposure to as low as 250 microg/L of cartap or 40 microg/L of cypermethrin. The mixture of both compounds showed no synergistic toxicity. The extremely high acute-to-chronic ratio suggests that the standard acute lethal toxicity assessment might not reflect the true environmental hazards of these frequently used pesticides. Ecological hazard assessments of long-term low dose or pulsed exposures to cartap and cypermethrin may reveal more realistic consequences of these compounds in surface water.     

Bioaccumulation of butyltins in Dreissena polymorpha at a confined placement facility in Buffalo, New York

This study involves a site characterization followed by biomonitoring with the zebra mussel, Dreissena polymorpha, at the Times Beach confined placement facility (CPF), located in Buffalo, NY. The contaminant of interest was tributyltin (TBT) and the degradation products dibutyltin (DBT) and monobutyltin (MBT). At study initiation (Day 0) TBT levels in the baseline mussels were 5.86 +/- 0.43 ng Sn/g, DBT levels were 2.25 +/- 0.37 ng Sn/g. No MBT was detected in the Day 0 baseline samples. Caged reference mussels placed back in the Black Rock Channel Lock and retrieved on Days 19 and 34 had TBT, DBT, and MBT levels which did not differ significantly from the Day 0 baseline levels. Mussels placed at the Times Beach CPF had TBT concentrations that were significantly lower at both Days 19 (3.65 +/- 0.90 ng Sn/g) and 34 (3.50 +/- 1.03 ng Sn/g) than the Day 0 baseline analysis (5.86 +/- 0.43 ng Sn/g). The results of this study indicate that butyltins were detected at the CPF site in the sediment (7.33 +/- 5.70 ng Sn/g) but not the water column (not detected at 0.01 microgram/l). In this study the zebra mussel was able to depurate TBT even in the presence of contaminated sediment. TBT may be bioaccumulated from the sediments. However, the initial levels in the mussels were so high, levels actually dropped as sediment-tissue equilibria levels were reached by the mussels.     

Exposure of Chironomus riparius larvae to uranium: effects on survival, development time, growth, and mouthpart deformities

Among non-biologically essential metals, data concerning uranium effects on freshwater benthic macroinvertebrates are scarce. The effects of uranium on survival, development time, growth and mouthpart deformities of midge Chironomus riparius were investigated. A 10-day static laboratory bioassay was performed exposing first instar larvae to artificial sediment spiked with four concentrations of uranium (2.97; 6.07; 11.44; 23.84 microg U g(-1) dry wt). As uranium was released from the sediment to the overlying water during this bioassay, both the sediment and the water column act as contamination pathways in giving rise to the observed effects. Significant negative effects on survival, development time, and growth were detected at 6.07, 6.07 and 2.97 microg U g(-1) dry wt, respectively. An LC20 of 2.49 microg U g(-1) dry wt (95% CI=1.48-4.27), and an LC50 of 5.30 microg U g(-1) dry wt (95% CI=3.94-7.25) were estimated. With respect to effects of uranium on larvae mouthpart deformities, we found that the lower the concentrations, the higher the deformity rates. These results highlight the potential impact of uranium at population level in environmentally realistic concentrations.     

Survey of organotin compounds in rivers and coastal environments in Portugal 1999-2000

In the period from April 1999 to May 2000, organotin pollution, namely butyl and phenyltins, was investigated in coastal and continental waters (46 stations), estuarine sediments (15 stations) and mussels (Mytilus galloprovincialis) (13 stations) throughout Portugal. Sampling points were chosen in areas of specific industrial, agricultural and harbor activities. Butyltins (BTs) were the only tin species identified of which tributyltin (TBT) was found in the whole area. Concentrations of TBT in river water ranged from 3 to 30 ng L(-1) (as Sn), marine sediment ranged from 4 to 12 microg kg(-1) (as Sn), whereas concentrations in mussel tissue ranged from 2.5 to 490 microg kg(-1) (as Sn). Given that some water samples appeared to be contaminated by higher monobutyltin (MBT) and dibutyltin (DBT) concentrations, the role of biological degradation and direct inputs from agricultural and industrial applications areas are discussed. The study compares depleted butyltin pollution in sediments and mussels of the Portuguese coastline associated with antifouling paints with previously reported levels. Inputs in river waters are more related to (i) PVC leaching and (ii) industrial sources, in some cases discharged by municipal wastewaters.     

Tributyltin accumulation and effects in marine molluscs from West Greenland

The levels of the antifouling agent tributyltin (TBT) and its breakdown products in bivalves were investigated in 1999-2000 at six areas along the west coast of Greenland with focus on locations inside and outside harbours. In addition female gastropods were examined for the development of TBT-induced masculine characteristics in form of imposex or intersex. The highest TBT concentration, 254 ng x g(-1) ww, was found in the bivalve Mytilus edulis sampled inside Nuuk harbour, but significant TBT concentrations were also present in bivalves from the other harbour areas. Only low levels of TBT were detected in bivalves sampled outside the harbours and in several of the samples the TBT level was below the detection limit. The examination of neogastropods like Buccinum revealed that imposex development occurred in all the harbours. In contrast, imposex was not found in any neogastropods sampled outside the harbour areas. However, the value of marine neogastropods as indicators of TBT contamination in West Greenland seems limited, because of large species diversity and the difficulties in sampling enough specimens at least with the current sampling strategy. No effects, which could be related to TBT contamination, were found in the most abundant tidal gastropod in West Greenland, Littorina saxatilis.     

Tributyltin distribution in the coastal environment of Peninsular Malaysia

The occurrence of tributyltin (TBT) is reported in the coastal waters of a few selected sites in Peninsular Malaysia. Water, bivalves and sediment samples collected were analysed specifically for TBT using sensitive analytical methods which involved a solvent extraction procedure with appropriate clean-up followed by graphite furnace atomic absorption spectrometric measurements. The levels of TBT in the seawater in unexposed areas were found in the range from <3.4 to 20 ng litre(-1) as compared to coastal areas with high boat and ship activities where TBT levels in seawater were generally above 30 ng litre(-1), with the highest level found at 281.8 ng litre(-1). TBT levels in the tissues of random cockle and soft-shell clam samples from local markets were found in the range from <0.5 to 3.7 ng g(-1) wet weight. The levels of TBT found in green mussel samples both from the market (23.5 ng g(-1) wet weight) and those from a mussel farm (14.2 ng g(-1) wet weight) indicate slight accumulation of TBT. In sediments, TBT levels were found ranging from <0.7 ng g(-1) dry weight in unexposed coastal sites to as high as 216.5 ng g(-1) dry weight for a site within a port area.     

Quantification of organotin compounds and determination of imposex in populations of dogwhelks (Nucella lapillus) from Norway

Unintentional effects of the antifouling agent tributyltin (TBT) have been discovered in marine gastropods as the induction of male sex characters in females, known as imposex. The occurrence of imposex in dogwhelks (Nucella lapillus) was investigated in 41 populations sampled in 1993-1995 along the Norwegian coast. A method for quantification of organotin species using gas chromatography and atomic emission detection (GC-AED) was developed. Some degree of imposex occurred in almost all populations of dogwhelks studied, except in four from Northern Norway. The concentration of organotin compounds in the gastropods from the unaffected populations was below the detection limit (7 ng Sn/g d.w.). The concentration of TBT in dogwhelks from affected populations was in the range 48-1096 ng Sn/g d.w. A positive relation between the concentration of TBT in dogwhelks and the degree of imposex was found.     

Toxicity of uranium and copper individually, and in combination, to a tropical freshwater macrophyte (Lemna aequinoctialis)

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27 degrees C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16+/-1.0 microg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 microg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758+/-35 microg l-1 with a MDEC of 112 microg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines.     

In-situ partitioning of butyltin compounds in estuarine sediments

The in-situ solid/pore-water partitioning of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) was determined for an estuarine sediment profile collected from a commercial marina. Total butyltin levels exceeded sediment quality guideline values, and were 220-8750 microg/kg for TBT, 150-5450 microg/kg for DBT and 130-4250 microg/kg for MBT. Pore-water butyltin concentrations ranged from 0.05 to 2.35 microg/l for TBT, 0.07-3.25 microg/l for DBT, and 0.05-0.53 microg/l for MBT. The partitioning of butyltin compounds between the sediment solid-phase and pore-water was described by an organic carbon normalised distribution ratio (D(OC)). The observed D(OC) values were similar for TBT, DBT and MBT, and were 10(5)-10(6) l/kg. Values for the Butyltin Degradation Index (BDI) were larger than 1 at depths greater than 10 cm below the sediment/water-column interface. This indicates that substantial TBT degradation has occurred in the sediments, and suggests that natural attenuation may be a viable sediment remediation strategy.