Ecotoxicity threshold values for 4-hydroxychlorothalonil, carbendazim, dimethoate and methoxyfenozide in fresh and marine waters: Part 1. Derivation of threshold values.

Pesticide active ingredients are frequently detected in the rivers, creeks, wetlands, estuaries, and marine waters of the Great Barrier Reef (GBR) region and are one of the main contributors to poor water quality. Pesticide concentrations detected in the environment through water quality monitoring programs can be compared against estimates of ecologically "safe" concentrations (i.e., water quality guidelines) to assess the potential hazard and risk posed to aquatic ecosystems. Water quality guidelines are also required to estimate the aquatic risk posed by pesticide mixtures, which is used for the Reef 2050 Water Quality Improvement Plan pesticide target. Seventy-four pesticide active ingredients and their degradates are frequently detected in GBR catchment waterways, however many do not have water quality guidelines in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The current study derives ecotoxicity threshold values (ETVs) as unendorsed guideline values for active ingredients in two fungicides (4-hydroxychlorothalonil (fungicide degradate) and carbendazim) and two insecticides (dimethoate and methoxyfenozide) that are commonly detected in GBR catchment waterways. The proposed ETVs have been derived using species sensitivity distributions, as recommended in the Australian and New Zealand nationally endorsed method for deriving water quality guidelines for aquatic ecosystem protection. Four ETVs were derived for each chemical with values that should theoretically protect 99, 95, 90 and 80 % of species (i.e., PC99, PC95, PC90, PC80, respectively). The PC99 and PC95 values for 4-hydroxychlorothalonil, carbendazim, dimethoate and methoxyfenozide were 0.49 µg/L and 4 µg/L, 0.029 µg/L and 0.45 µg/L, 0.11 µg/L and 5.8 µg/L and 0.19 µg/L and 2 µg/L, respectively. The ETVs will be used in an ecological hazard and risk assessment across GBR waterways in part two of this study. The ETVs can also be used to assess potential risk across Australia and internationally where monitoring data are available.

Secondary vitellogenesis persists despite disrupted fecundity in amphipods maintained on metal-contaminated sediment: X-ray fluorescence assessment of oocyte metal content.

Melita plumulosa is an epibenthic, detritivorous amphipod found in estuaries along the eastern coast of Australia. It has been utilized as a test organism in rapid ten to thirteen days reproduction toxicity tests for sediment quality assessment. The fecundity of females in the toxicity test has been found to be inhibited by exposure of the amphipods to contaminated sediments enriched with zinc and other metals. This study investigated the proposal that interference in vitellogenesis is the cause of reproductive toxicity of metals in crustaceans. Inspection of the ovaries from amphipods on day 6 of the test either from control or Zn/Pb/Cd/Cu-spiked sediment, that were nearing completion of vitellogenesis, showed that the females in all treatments were producing similar numbers of oocytes undergoing secondary vitellogenesis. The distribution of the Zn, Cu and Pb in the oocytes and ventral caeca of females was examined by X-ray fluorescence microscopy. Elemental mapping revealed a dense accumulation of Zn in primary oocytes and a uniform distribution of Zn and Cu in the secondary oocytes in all treatments. Zn and Cu were also observed to be uniformly distributed in the ventral caeca. Pb was not detected in either of these tissues. The apparent normal morphology and the typical number of oocytes undergoing secondary vitellogenesis suggest that vitellogenesis was not being disrupted by Pb displacing Zn in the metal-binding domain of vitellogenin in amphipods exposed to the contaminated sediment during the test. Alternative mechanisms for the reproductive toxicity of amphipods exposed for six days to metal-contaminated sediment are discussed.

Thyroid disruption in the lizard Podarcis bocagei exposed to a mixture of herbicides: a field study.

Pesticide exposure has been related with thyroid disrupting effects in different vertebrate species. However, very little is known about the effects of these compounds in reptiles. In the Mediterranean area, lacertid lizards are the most abundant vertebrate group in agroecosystems, and have been identified as potential model species for reptile ecotoxicology. The aim of this study was to understand if the herbicides applied in corn fields have thyroid disruptive effects in the lizard Podarcis bocagei. Adult male lizards were captured in north-western Portugal in corn fields treated with herbicides (exposed sites), and in organic agricultural fields (reference sites). Thyroid and male gonad morphology and functionality, and testosterone levels were investigated through histological, immunohistochemical and biochemical techniques. Lizards from exposed locations displayed thyroid follicular lumens with more reabsorption vacuoles and significantly larger follicular area than those from reference fields. Furthermore, testes of lizards from exposed locations had significantly larger seminiferous tubule diameters, significantly higher number of spermatogenic layers and displayed an up-regulation of thyroid hormone receptors when compared with lizards from reference areas. These findings strongly suggest that the complex mixture of herbicides that lizards are exposed to in agricultural areas have thyroid disrupting effects which ultimately affect the male reproductive system. Alachlor, which has demonstrated thyroid effects in mammals, may be largely responsible for the observed effects.

Detecting long temporal trends of photosystem II herbicides (PSII) in the Great Barrier Reef lagoon.

The Marine Monitoring Program (MMP) was established in 2005 to monitor the inshore health of the Great Barrier Reef (GBR) and evaluate progress towards water quality objectives in Reef Water Quality Improvement Plans. The MMP provides information on the magnitude and spatial extent of pesticide contamination, reports on temporal variability, and provides a risk assessment for the biota in the GBR lagoon. However, long-term trends in pesticide contamination of inshore marine waters over the entire monitoring period (2005-2018) have not been assessed. We used up to 14 years of monitoring data for five PSII herbicides (ametryn, atrazine, diuron, tebuthiuron, and hexazinone) to conduct temporal trend analyses at 11 inshore monitoring sites. The trend analyses suggested increasing significant trends (p < 0.05) for the five PSII herbicides concentrations at several monitoring sites. Power analysis indicated that monitoring sites with over 10 years of monitoring data had convincing results with 80% power.

Hormonal induction of spermiation, courting behavior and spawning in the southern bell frog, Litoria raniformis.

We trialled the efficacy of various exogenous hormones to induce spermiation, courtship behavior, and spawning in the "endangered" southern bell frog, Litoria raniformis. Intralymphatic administration of Lucrin(®), a synthetic nonapeptide luteinizing hormone releasing hormone (LHRH), was used successfully to induce courting behaviors and ejaculation of spermatozoa in males. Various hormones, including Lucrin(®), another synthetic LHRH analog ([des-Gly(10), D-Ala(6)]-LHRH), human chorionic gonadotropin, progesterone, and a dopamine receptor antagonist failed to promote oviposition and spawning in females. This and earlier studies indicate that in the efficacy of hormonal induction in amphibians varies between taxa, hormones, and genders. The lack of response in females may limit the use of reproduction technology in the southern bell frog and closely related species of Australian bell frogs.

Development and application of a rapid amphipod reproduction test for sediment-quality assessment.

Melita plumulosa is an epibenthic, detritivorous amphipod native to eastern Australia that has been adopted as a test organism for toxicity evaluations of contaminated estuarine sediments. In the present study, a 13-d amphipod reproduction test was developed that encompasses gametogenesis, fertilization, and embryo development before hatching. The primary endpoints for the test are fecundity (measured as the number of embryos per individual surviving female) and a fecundity index (fecundity multiplied by the stage of embryo development). This new test has been employed to scrutinize the sediments from a metal-contaminated coastal lagoon. Lake Macquarie (NSW, Australia) is a large, saltwater lagoon that has received metal pollution over many decades, leading to a concentration gradient of trace metals, including Pb, Zn, Cd, and Cu, in the sediments. Within one of the northern bays (Warners Bay), the concentrations of these metals either border on or exceed sediment quality guideline values prescribed by Australian and New Zealand Guidelines for Fresh and Marine Water Quality. In trials with the 13-d amphipod reproduction test, Warners Bay sediments significantly reduced fecundity in the test species. Subsequent tests with clean sediments spiked singly with Pb, Zn, or Cu indicated that no single metal was responsible for the observed toxicity in the field sediments. However, sediments spiked with various combinations of Pb, Zn, Cd, and Cu indicated that Zn in combination with one or more of the other metals was responsible for the reproductive toxicity observed in Warners Bay sediments. In all these tests, measured metal concentrations in overlying water and pore water were low, thus confirming that the observed effects on reproduction could be attributed to dietary exposure to metals.

Fatty acid composition of the estuarine amphipod, Melita plumulosa (Zeidler): link between diet and fecundity.

The influence of various diets on the survival, fecundity, and the polyunsaturated fatty acid (PUFA) composition of the benthic estuarine amphipod Melita plumulosa (Zeidler) in laboratory cultures were determined. Apart from a natural silty sediment, six commercial food supplements were examined: an omega-6 PUFA enriched Spirulina-based dry powder, Sera micron; a shrimp-based pellet food; an omega-3 PUFA enriched algal paste, Rotiselco-ALG; an omega-6 PUFA enriched algal dry powder, AlgaMac-ARA (arachidonic acid); flaxseed meal; and an omega-3 PUFA enriched dry powder, Frippak. We have previously established that M. plumulosa cultures perform poorly and eventually decline if provided with silty sediment alone, but will thrive if supplemented with Sera micron. Conversely, if the amphipods are cultured on a nutrient-depleted sand substrate, Sera micron alone does not constitute an adequate feed. The major difference in the fatty acid composition of M. plumulosa cultured on silty sediment compared to amphipods cultured on a sand substrate and both fed Sera micron was an increase in the ratio of omega-3 to omega-6 PUFAs, indicating that the silty sediment provides additional food sources rich in omega-3 PUFAs. Furthermore, amphipods cultured in sand and fed any of the three algal-based foods or the Frippak powder as the sole food source had poor survival rates, although Sera micron maintained the best survival-this was attributed to it containing high amounts of beta-carotene and terpenoids. Melita plumulosa fed a mixture of Sera micron in conjunction with the omega-3 PUFA enriched Rotiselco-ALG and cultured on a silty substrate were found to have good fecundity with low variability.

Genetic and life-history trait variation of the amphipod Melita plumulosa from polluted and unpolluted waterways in eastern Australia.

To monitor genetic diversity and environmental contamination in eastern Australia, toxicity studies have employed the sensitive benthic amphipod Melita plumulosa. The goal of this study was to examine the genetic and life-history variability of natural populations of M. plumulosa from the Parramatta (polluted) and Hawkesbury (unpolluted) Rivers. The underlying genetics of the populations in these distinct waterways was examined at one mitochondrial (cytochrome c oxidase subunit I (COI)) and one nuclear (ribosomal internal transcribed spacer region 1 (ITS1)) locus. Seven unique haplotypes for COI were found amongst animals from the Parramatta River, while animals from the Hawkesbury River showed a complete absence of genetic variation at this locus. At ITS1 a total of two sequence variants were found amongst Parramatta River amphipods and three sequence variants among Hawkesbury River animals, with no common variants across the two river systems. To establish whether genetic differences were associated with organismal responses to toxicant exposure, two life-history trait variables (female head length as an estimator of amphipod size and female fecundity) were analyzed. Life-history trait analyses showed that females from the Hawkesbury River were significantly larger and more fecund. These data have critical implications for toxicity tests, the use of laboratory cultures for testing purposes, and environmental contamination in Sydney Harbor.

Does subcellular distribution in plants dictate the trophic bioavailability of cadmium to Porcellio dilatatus (Crustacea, Isopoda)?

The present study examined how subcellular partitioning of Cd in plants with different strategies to store and detoxify Cd may affect trophic transfer of Cd to the isopod Porcellio dilatatus. The plant species used were Lactuca sativa, a horticultural metal accumulator species; Thlaspi caerulescens, a herbaceous hyperaccumulator species; and the nonaccumulator, T. arvense. Taking into account that differences in subcellular distribution of Cd in plants might have an important role in the bioavailability of Cd to a consumer, a differential centrifugation technique was adopted to separate plant leaf tissues into four different fractions: cell debris, organelles, heat-denatured proteins, and heat-stable proteins (metallothionein-like proteins). Plants were grown in replicate hydroponic systems and were exposed for 7 d to 100 microM Cd spiked with 109Cd. After a 14-d feeding trial, net assimilation of Cd in isopods following consumption of T. caerulescens and T. arvense leaves reached 16.0 +/- 2.33 and 21.9 +/- 1.94 microg/g animal, respectively. Cadmium assimilation efficiencies were significantly lower in isopods fed T. caerulescens (10.0 +/- 0.92%) than in those fed T. arvense (15.0 +/- 1.03%). In further experiments, Cd assimilation efficiencies were determined among isopods provided with purified subcellular fractions of the three plants. On the basis of our results, Cd bound to heat-stable proteins was the least bioavailable to isopods (14.4-19.6%), while Cd bound to heat-denatured proteins was the most trophically available to isopods (34.4-52.8%). Assimilation efficiencies were comparable in isopods fed purified subcellular fractions from different plants, further indicating the importance of subcellular Cd distribution in the assimilation. These results point to the ecological relevance of the subcellular Cd distribution in plants, which directly influence the trophic transfer of Cd to the animal consumer.

Bioaccumulation of Cd by a European lacertid lizard after chronic exposure to Cd-contaminated food.

Apart from analyses for elemental contaminants in field collected specimens, very little is known about the assimilation, accumulation and toxic effects of inorganic contaminants in reptiles. This study examined the chronic accumulation of Cd in a European lacertid lizard (Podarcis carbonelli) following dietary provision of an environmentally realistic concentration of Cd for 21 weeks. Lizards were provided with Cd that had either been biologically incorporated into crickets, or as Cd(NO3)2 added superficially to crickets just prior to feeding. Among both treatment groups Cd accumulated in tissues in the following order of concentration: gut>liver>kidney>carcass. The majority of the Cd was retained within the gut, and transfer to internal organs was low. Morphological indices, brain and plasma cholinesterase activities, gut and liver metallothionein content, and standard metabolic rate were measured as biomarkers of exposure and effect; however, no differences between control lizards and Cd-treated lizards were observed.

Cadmium assimilation in the terrestrial isopod, Porcellio dilatatus--is trophic transfer important?

Terrestrial isopods have become important tools for the ecotoxicological assessment of metal-contaminated soils. Their value as an invertebrate model is partly because of their extraordinary capacity to bioaccumulate toxic metals from the environment. Replication of this accumulation process in the laboratory has in the past relied on the amendment of organic food substrates through the addition of inorganic metal salts. However, the bioavailability of the metals when presented through doping regimes may differ from the bioavailability of metals in nature, because over time metals become biologically compartmentalised and form complexes with organic molecules. This study examines the differential bioavailability of Cd to the terrestrial isopod, Porcellio dilatatus, when presented as either a Cd-amended diet or pre-incorporated biologically into lettuce (Lactuca sativa). Isopods were either provided with lettuce contaminated superficially with Cd(NO(3))(2) or lettuce grown hydroponically in growth media containing 100 microM Cd(NO(3))(2). Assimilation efficiency of Cd was greater among isopods that were fed the amended diet (71%, S.E.=7%), than among isopods feeding on biologically contaminated lettuce (52%, S.E.=5%) and demonstrates that speciation of Cd is likely to influence the rate of Cd assimilation and accumulation in a laboratory test.

Assimilation of cadmium in a european lacertid lizard: Is trophic transfer important?

Apart from analyses for elemental contaminants in field-collected specimens, very little is known about the assimilation and accumulation of inorganic contaminants in reptiles. Recent dietary studies with reptiles (and some other vertebrates and invertebrates) have taken care to incorporate the principles of trophic transfer by pre-exposing prey items to the elemental contaminant of interest. However, there are conflicting data in the literature as to whether biologically incorporated metals are more bioavailable to consumers in a food chain than simple salts added to the diet, and this study examines this issue in a lacertid lizard. Adult individuals of Podarcis carbonelli were exposed to cadmium (Cd) in a 21-week dietary study to determine whether the form in which the Cd is provided influences assimilation efficiency for this metal. Lizards were provided with Cd that had either been biologically incorporated into crickets or as Cd(NO3)2 added superficially to crickets just prior to feeding. Radiospectrometric analysis for 109Cd in animal tissues and fecal material was used to follow Cd accumulation over the duration of exposure. The highest levels of accumulation were found within the gut. This, combined with the observation of higher rates of assimilation over the first five weeks, strongly suggests a rapid accumulation of Cd within the gut tissue followed by a slower redistribution to other tissues. No statistically different levels of Cd assimilation efficiency were detected between the two treatment groups, nor were there any statistically significant differences between the two treatment groups in relation to the proportional distribution to the gut, liver, or kidneys.

Biologically incorporated dietary silver has no ionoregulatory effects in American red crayfish (Procambarus clarkii).

Two silver-contaminated diets were prepared by exposing juvenile rainbow trout for 8 d to waterborne silver thiosulfate as Ag at either 0.1 microg/L (low-Ag diet) or 80 mg/L (high-Ag diet). The level of total Ag accumulated in whole low-Ag fish was below the detection limit of analysis. Whole high-Ag fish accumulated Ag at 21.3 nmol/g. The livers of the low- and high-Ag fish accumulated Ag at 0.43 nmol/g and 1.01 micromol/g, respectively. The Ag-contaminated fish were then fed whole to adult crayfish in an 80-d dietary study to determine the effects of long-term trophic accumulation of Ag. In a second experiment, the livers of the high-Ag trout were fed to juvenile crayfish for either one or five weeks. Accumulation of Ag was demonstrated in both adult and juvenile crayfish. Silver accumulation in juvenile crayfish peaked at approximately 650 nmol/g at three weeks, after which Ag depuration occurred. In adult crayfish that consumed the high-Ag diet, the hepatopancreas accumulated more than 90% of assimilated Ag, rising 1,000-fold over control animals to approximately 740 nmol/g at 80 d. Crayfish that consumed the low-Ag diet had small, statistically insignificant elevations of Ag in some tissues. Dietary Ag had no effect on juvenile crayfish growth or adult mortality. Disturbances in osmoregulation, which are normally associated with acute waterborne Ag exposure, were not detected. Dietary Ag also had no effect on hemolymph concentrations of Na+, Cl-, Ca2+, Mg2+, or Cu; did not affect the concentration kinetics of Na+ or Cl- influx; and had no effect on the activity of gill Na+/K+-dependent adenosine triphosphatase. Hemolymph concentrations of glucose and lactate were similarly unaffected, indicating an absence of stress-related metabolic disturbance. However, a disproportionately low number of ecdysis events occurred among crayfish that consumed the high-Ag diet.

Evaluation of the protective effects of reactive sulfide on the acute toxicity of silver to rainbow trout (Oncorhynchus mykiss).

Acute 96-h toxicity tests were performed with juvenile rainbow trout (Oncorhynchus mykiss) exposed to AgNO3 in either the absence or the presence of 100 nM reactive sulfide to evaluate the protective effect of aqueous sulfides against ionic Ag toxicity. The sulfide was presented in the form of zinc sulfide (ZnS) clusters under oxic conditions. Silver was lost from the water column during the course of the experiment, so mean measured Ag concentrations were used to generate all median lethal concentration (LC50) data. The system was complicated in that Ag2S precipitated because of the need for large amounts of Ag to obtain lethal effects in the presence of ZnS. Some of the losses of Ag could be explained by complexation with ZnS and formation of solid Ag2S. Other losses were probably the result of partial adsorption to exposure-chamber walls or to complexation with ligands or functional groups within organic material produced by the fish. The LC50 (95% confidence interval) values generated using measured concentrations for total Ag were 139 (122-162) nM in the absence of sulfide and 377 (340-455) nM in the presence of 100 nM sulfide. The LC50 values generated using measured concentrations from filtered (pore size, 0.45 microm) water samples were 122 (105-145) nM in the absence of sulfide and 225 (192-239) nM in the presence of 100 nM sulfide. These results suggest a stoichiometric protection of sulfides up to a 2:1 ratio of Ag:sulfide. Greater accumulation of Ag at the gills was measured in fish exposed to AgNO3 in the presence of sulfide.

The use of a lacertid lizard as a model for reptile ecotoxicology studies--part 1 field demographics and morphology.

At the European level, lacertid lizards have been proposed as potential model species for reptile ecotoxicology. We studied demographic and morphological aspects of natural field subpopulations of Podarcis bocagei inhabiting similar agricultural habitats which were either regularly exposed to pesticides, or not. Parameters examined in this study included population size and density, sex ratio, adult body size, fluctuating asymmetry in femoral pores and parasite prevalence. In general, we detected few statistically significant differences between the exposed and reference subpopulations. Although field situations are ecologically complex and factors other than pesticides may be acting, the absence of observable effects on field subpopulations is probably indicative that lizards are coping or compensating for this level of exposure.

The use of a lacertid lizard as a model for reptile ecotoxicology studies: part 2--biomarkers of exposure and toxicity among pesticide exposed lizards.

As part of a wider study examining the impacts of corn pesticides on lacertid lizards in north-western Portugal, we examined various physiological, biochemical, and histological biomarkers of exposure and effect among field populations of Podarcis bocagei. Biomarkers included body condition index, standard metabolic rate, locomotor performance, parasitization, glutathione oxidative pathways and related enzyme activity, lipid peroxidation and liver and testis histology. Few of the various biomarkers investigated provided statistically significant evidence of toxic effect. However, using a weight of evidence approach, we conclude that pesticides are affecting lizards living in the vicinity of pesticide exposed corn agriculture sites. Lizards from these locations present a profile of animals under metabolic stress with reduced condition indices, increased standard metabolic rate, lower incidence of hepatocyte vacuolation, altered iron metabolism, increased activation of GSH oxidation pathways, and even increased prevalence of hemoparasites.

Biomarkers of exposure and effect in a lacertid lizard (Podarcis bocagei Seoane) exposed to chlorpyrifos.

In Europe, reptiles have been recently included in environmental risk-assessment processes for registration of plant-protection products. However, data on toxicity effects of most compounds are lacking. Chlorpyrifos is the most commonly used organophosphorus insecticide worldwide. In the present study, the authors exposed a lacertid lizard, Podarcis bocagei, to sublethal concentrations of chlorpyrifos. Individuals were exposed through spiked food for a period of 20 d (low dose 0.12 mg/kg/d, high dose 1.57 mg/kg/d). After exposure, various biomarkers of exposure and effect were evaluated, including the activities of glutathione S-transferase and enzymes involved in the glutathione redox cycle, glutathione concentrations, activities of esterases, liver and testes histopathologies, as well as locomotory and predatory behavior. The results indicate that sublethal, subchronic exposure to chlorpyrifos can affect P. bocagei in a dose-dependent manner. Adverse effects occurred at both the subindividual and individual levels, including inhibition of carboxylesterases and cholinesterases (ChEs), liver histopathological changes, and altered predatory behaviors. Animals exposed to chlorpyrifos took more time to capture and subdue prey items. The results suggest a link between effects at subindividual levels of organization with those observed at the whole individual level after exposure to environmentally realistic dosages of chlorpyrifos.

Temporal and geographical genetic variation in the amphipod Melita plumulosa (Crustacea: Melitidae): Link of a localized change in haplotype frequencies to a chemical spill.

Anthropogenic effects such as contamination affect the genetic structure of populations. This study examined the temporal and geographical patterns of genetic diversity among populations of the benthic crustacean amphipod Melita plumulosa in the Parramatta River (Sydney, Australia), following an industrial chemical spill. The spill of an acrylate/methacrylate co-polymer in naphtha solvent occurred in July 2006. M. plumulosa were sampled temporally between December 2006 and November 2009 and spatially in November 2009. Genetic variation was examined at the mitochondrial cytochrome c oxidase subunit I locus. Notably, nucleotide diversity was low and Tajima's D was significantly negative amongst amphipods collected immediately downstream from the spill for 10 months. We hypothesize that the spill had a significant localized effect on the genetic diversity of M. plumulosa. Alternate explanations include an alternate and unknown toxicant or a localized sampling bias. Future proposed studies will dissect these alternatives.

Foraging, feeding, and reproduction on silica substrate: Increased waterborne zinc toxicity to the estuarine epibenthic amphipod Melita plumulosa.

Artificial substrates consisting of fine milled silica with or without α-cellulose were evaluated for their capacity to support survival, growth, and fecundity in the amphipod Melita plumulosa. There were no significant differences in the survival and fecundity of adult amphipods maintained for up to 13 d on natural sediment, silica-only, or silica/α-cellulose substrate when fed two algal foods, Sera micron and Rotiselco-ALG. However, growth among juveniles maintained on the silica/α-cellulose mixture was significantly inhibited over 14 d compared with natural sediment. Addition of a microencapsulated shrimp feed, Frippak, to the algal foods improved juvenile growth over 28 d but still did not match the nutritive value of natural sediment. Fine silica without cellulose was subsequently used in acute and reproductive toxicity tests with waterborne zinc. With food, a 10-d median lethal concentration (LC50) of 140 µg Zn/L and a 10-d no-effect concentration (NEC) of 80 µg Zn/L were obtained for juvenile survival on silica. In contrast, a 10-d LC50 of 200 µg Zn/L and a 10-d NEC of 180 µg Zn/L were obtained for juveniles in water-only exposures. Similarly, exposure of adult females to Zn without food on silica compared with water-only exposures gave 10-d LC50s of 380 and 490 µg Zn/L and 10-d NECs of 130 and 370 µg Zn/L, respectively. The reproduction toxicity test indicated significant adult mortality at 92 µg Zn/L and significantly reduced fecundity at 22 µg Zn/L. We surmised that the toxicity of waterborne zinc to M. plumulosa increased when maintained on nutrient-depleted silica compared with water-only exposure because of increased energy expended through foraging, in concert with the likely increased exposure to Zn via the digestive tract and the gills.

The influence of metal speciation on the bioavailability and sub-cellular distribution of cadmium to the terrestrial isopod, Porcellio dilatatus.

Cadmium is a non-essential toxic metal that is able to bioaccumulate in both flora fauna and has the potential to biomagnify in some food chains. However, the form in which cadmium is presented to consumers can alter the bioavailability and possibly the internal distribution of assimilated Cd. Previous studies in our laboratory highlighted differences in Cd assimilation among isopods when they were provided with a plant-based food with either Cd biologically incorporated into plant tissue or superficially amended with ionic Cd(2+). Cd is known for its high affinity for sulphur ligands in cysteine residues which form the basis for metal-binding proteins such as metallothionein. This study compares Cd assimilation efficiency (AE) in Porcellio dilatatus fed with food amended with either cadmium cysteinate or cadmium nitrate in an examination of the influence of Cd speciation on metal bioavailability followed by an examination of the sub-cellular distribution using a centrifugal fractionation protocol. As hypothesized the AE of Cd among isopods fed with Cd(NO(3))(2) (64%, SE=5%) was higher than AE for isopods fed with Cd(Cys)(2) (20%, SE=3%). The sub-cellular distribution also depended on the Cd species provided. Those isopods fed Cd(Cys)(2) allocated significantly more Cd to the cell debris and organelles fractions at the expense of allocation to metal-rich granules (MRG). The significance of the difference in sub-cellular distribution with regard to toxicity is discussed. This paper demonstrates that the assimilation and internal detoxification of Cd is dependent on the chemical form of Cd presented to the isopod.