Bioaccumulation of mining derived metals in blood, liver, muscle and otoliths of two Arctic predatory fish species (Gadus ogac and Myoxocephalus scorpius).

Mining activities can cause adverse and long-lasting environmental impacts and detailed monitoring is therefore essential to assess the pollution status of mining impacted areas. Here we evaluated the efficacy of two predatory fish species (Gadus ogac i.e. Greenland cod and Myoxocephalus scorpius i.e. shorthorn sculpin) as biomonitors of mining derived metals (Pb, Zn, Cd and Hg) by measuring concentrations in blood, liver, muscle and otoliths along a distance gradient near the former Black Angel Pb-Zn mine (West Greenland). We detected metals in all tissues (except Cd and Hg in otoliths) and sculpin generally displayed higher concentrations than cod. For both species, concentrations were generally highest closest to the dominant pollution source(s) and gradually decreased away from the mine. The clearest gradient was observed for Pb in blood and liver (both species), and for Pb in otoliths (sculpin only). Similar to dissolved concentrations in seawater (but in contrast to bottom sediment), no significant decrease was found for Zn, Cd and Hg in any of the tissues. This demonstrates that by including tissues of blood (representing recent accumulation) and otolith (representing more long-term exposure signals) in the sampling collection, the temporal information on contaminant exposure and accumulation can be extended. We therefore conclude that both fish species are suitable as biomonitors near Arctic mine sites and, moreover, that blood and otoliths can serve as important supplementary monitoring tissues (in addition to liver and muscle traditionally sampled) as they provide extended temporal information on recent to long-term contaminant exposure.

Improved physiologically based pharmacokinetic model for oral exposures to chromium in mice, rats, and humans to address temporal variation and sensitive populations.

A physiologically based pharmacokinetic (PBPK) model for hexavalent chromium [Cr(VI)] in mice, rats, and humans developed previously (Kirman et al., 2012, 2013), was updated to reflect an improved understanding of the toxicokinetics of the gastrointestinal tract following oral exposures. Improvements were made to: (1) the reduction model, which describes the pH-dependent reduction of Cr(VI) to Cr(III) in the gastrointestinal tract under both fasted and fed states; (2) drinking water pattern simulations, to better describe dosimetry in rodents under the conditions of the NTP cancer bioassay; and (3) parameterize the model to characterize potentially sensitive human populations. Important species differences, sources of non-linear toxicokinetics, and human variation are identified and discussed within the context of human health risk assessment.

Methylmercury Induced Neurotoxicity and the Influence of Selenium in the Brains of Adult Zebrafish (Danio rerio).

The neurotoxicity of methylmercury (MeHg) is well characterised, and the ameliorating effects of selenium have been described. However, little is known about the molecular mechanisms behind this contaminant-nutrient interaction. We investigated the influence of selenium (as selenomethionine, SeMet) and MeHg on mercury accumulation and protein expression in the brain of adult zebrafish (Danio rerio). Fish were fed diets containing elevated levels of MeHg and/or SeMet in a 2 × 2 full factorial design for eight weeks. Mercury concentrations were highest in the brain tissue of MeHg-exposed fish compared to the controls, whereas lower levels of mercury were found in the brain of zebrafish fed both MeHg and SeMet compared with the fish fed MeHg alone. The expression levels of proteins associated with gap junction signalling, oxidative phosphorylation, and mitochondrial dysfunction were significantly (p < 0.05) altered in the brain of zebrafish after exposure to MeHg and SeMet alone or in combination. Analysis of upstream regulators indicated that these changes were linked to the mammalian target of rapamycin (mTOR) pathways, which were activated by MeHg and inhibited by SeMet, possibly through a reactive oxygen species mediated differential activation of RICTOR, the rapamycin-insensitive binding partner of mTOR.

Genetic damage induced by electronic waste leachates and contaminated underground water in two prokaryotic systems.

The inappropriate and unsafe management practices related to disposal and recycling of electronic wastes in Nigeria has led to environmental and underground water contamination. Reports on the level and type of contamination as well as the possible DNA damage effects of this contamination are insufficient. This study evaluated the DNA damaging potential of e-waste simulated and raw leachates, and its contaminated underground water using the SOS chromotest on Escherichia coli PQ37 and the Ames Salmonella fluctuation test on Salmonella typhimurium strains TA98 and TA100, without and with metabolic activation. Physico-chemical parameters of the samples were also analyzed. The result of the Ames test showed induction of base pair substitution and frameshift mutation by the test samples. However, the TA100 was the more responsive strain for the three samples in terms of mutagenic index in the absence and presence of metabolic activation. The SOS chromotest results were in agreement with those of the Ames Salmonella fluctuation test. Nevertheless, the E. coli PQ37 system was slightly more sensitive than the Salmonella assay for detecting genotoxins in the tested samples. Lead, cadmium, manganese, copper, nickel, chromium, arsenic, and zinc contents analyzed in the samples were believed to play a significant role in the observed DNA damage in the microbial assays. The results of this study showed that e-waste simulated and raw leachates, and its contaminated underground water are of potential mutagenic and genotoxic risks to the exposed human populace.

Chemical techniques for assessing bioavailability of sediment-associated contaminants: SPME versus Tenax extraction.

The traditional approach for predicting the risk of hydrophobic organic contaminants (HOCs) in sediment is to relate organic carbon normalized sediment concentrations to body residues or toxic effects to organisms. However, due to the multiple variables controlling bioavailability, this method has limitations. A matrix independent method of predicting bioavailability needs to be used in order to be universally applicable. Both chemical activity (freely dissolved chemical concentrations) measured by solid-phase microextraction (SPME) and bioaccessibility (rapidly desorbing fraction) estimated by Tenax extraction have been developed to predict bioavailability of sediment-associated HOCs. The objectives of this review are to summarize a number of studies using matrix-SPME or Tenax extraction to estimate bioavailability and/or toxicity of different classes of HOCs and evaluate the strengths and weakness of these two techniques. Although the two chemical techniques assess different components of the matrix, estimates obtained from both techniques have been correlated to organism body residues. The advantages of SPME fibers are their applicability for use in situ and their potential usage for a wide array of contaminants by selection of appropriate coatings. Single time-point Tenax extraction, however, is more time- and labor-effective. Tenax extraction also has lower detection limits, making it more applicable for highly toxic contaminants. This review also calls for additional research to evaluate the role of sequestrated contaminants and ingestion of sediment particles by organisms on HOC bioavailability. The use of performance reference compounds to reduce SPME sampling time and linking chemical based bioavailability estimates to toxicological endpoints are essential to expand the applications of these methods.

Similarities and differences of metal distributions in the tissues of molluscs by using multivariate analyses.

Multivariate analysis including correlation, multiple stepwise linear regression, and cluster analyses were applied to investigate the heavy metal concentrations (Cd, Cu, Fe, Ni, Pb, and Zn) in the different parts of bivalves and gastropods. It was also aimed to distinguish statistically the differences between the marine bivalves and the gastropods with regards to the accumulation of heavy metals in the different tissues. The different parts of four species of bivalves and four species of gastropods were obtained and analyzed for heavy metals. The multivariate analyses were then applied on the data. From the multivariate analyses conducted, there were correlations found between the soft tissues of bivalves and gastropods, but none was found between the shells and the soft tissues of most of the molluscs (except for Cerithidea obtusa and Puglina cochlidium). The significant correlations (P < 0.05) found between the soft tissues were further complemented by the multiple stepwise linear regressions where heavy metals in the total soft tissues were influenced by the accumulation in the different types of soft tissues. The present study found that the distributions of heavy metals in the different parts of molluscs were related to their feeding habits and living habitats. The statistical approaches proposed in this study are recommended for use in biomonitoring studies, since multivariate analyses can reduce the cost and time involved in identifying an effective tissue to monitor the heavy metal(s) bioavailability and contamination in tropical coastal waters.

Metallothionein role in the kinetic model of copper accumulation and elimination in the clam Ruditapes decussatus.

In order to clarify the role of metallothioneins (MT) in copper (Cu) toxicity, this work aimed to assess the involvement of this protein in the accumulation and elimination strategies of Cu in the clam Ruditapes decussatus exposed to two sublethal concentrations (25 and 50 microgCul(-1)). The behaviour of MT in three different tissues of clams during the accumulation and depuration processes was also followed by gel-filtration chromatography to assess if Cu was bound to MT or to other cytosolic components. The 96 h LC50 for water-borne copper was 715 microgL(-1) in R. decussatus. The Cu accumulation pattern was dependent on Cu exposure concentrations. In clams exposed to 25 microgl(-1), total Cu accumulation in the three tissues increased linearly during the exposure period, while in those exposed to 50 microgl(-1) it followed the first order kinetic model. The greatest amount of Cu accumulated in all tissues is associated to the low molecular weight cytosolic fraction (>50%). The chromatographic assay indicated that Cu in the cytosolic fraction is bound to MT and MT levels increase with the increase of Cu exposure confirming the binding affinity of Cu to MT in all tissues. However, a smaller percentage of Cu seems to be bond to other ligands, such as GSH. Copper was exponentially eliminated (only studied in clams exposed to 25 microgl(-1)) and the estimated half-life was tissue dependent (9, 5 and 14 days for the gills, digestive gland and remaining tissues, respectively). Copper bound to the thermostable compounds was eliminated more quickly (t(1/2)=4-7 days) in all tissues than those bound to the thermolabile compounds (t(1/2)=7-18 days). Interestingly, MT is rapidly degraded (t(1/2)=7 and 18 days), suggesting that this protein is actively involved in the elimination of this metal, through the Cu-MT complex since MT and Cu are turning over simultaneously. Therefore, when Cu exposure is low, the clam can cope efficiently with the excess of Cu levels by increasing MT induction as well as rapidly eliminating this metal via the MT-Cu complex. Copper toxicity in the clam R. decussatus is associated to the limited capacity of MT induction at higher and environmental unrealistic Cu exposures especially in the gills and remaining tissues.

Overwinter alterations in energy stores and growth in juvenile fishes inhabiting areas receiving metal mining and municipal wastewater effluents.

The winter stress syndrome hypothesis proposes that the combination of winter conditions and contaminant exposure reduces overwinter survival in juvenile fishes, mainly due to increased depletion of stored energy (lipids). To test this hypothesis in the field, juvenile fathead minnows (Pimephales promelas), creek chub (Semotilus atromaculatus), and white sucker (Catostomus commersoni) were collected from three exposure sites along Junction Creek, Sudbury, Ontario, Canada, representing cumulative inputs from metal mining and municipal wastewater. Overwinter survival potential was determined through measurements of growth (length, weight, muscle RNA/DNA ratio, muscle proteins) and energy stores (whole body triglycerides) in fish collected just prior to and following the overwinter period. We hypothesized that fish collected from exposure sites would exhibit reduced growth and energy storage compared to reference fish in both fall and spring, and that fish from all sites would exhibit reduced energy storage in spring compared to the previous fall. Whole body Se concentrations were elevated (11-42 microg/g dry wt) in juvenile fathead minnows and white sucker collected at two exposure sites in comparison to fish collected from the reference site (3-6 microg/g dry wt). In contrast to our hypothesis, fathead minnows were larger with greater triglyceride stores at exposure sites compared to the reference site. White suckers were smaller at exposure sites but did not differ in triglycerides among sites. Overall, the results in these fish species exposed to metal mining and municipal wastewaters do not support the winter stress syndrome hypothesis. It is recommended that future studies focus on relating growth and energy storage with other environmental factors such as habitat and food availability in addition to anthropogenic contamination.

Heavy metals in fish from lakes in Latvia: concentrations and trends of changes.

The purpose of this study was to evaluate the level of heavy metal contamination of perch (Perca fluviatilis) from inland waters in Latvia. The level of metal (Cd, Cu, Co, Pb, Ni, Mn, Zn, Fe) accumulation in fish tissues (muscle, liver, and gills) relative to contamination level, gender, age, and tissue type were studied in fish samples from 14 bog (dystrophic) lakes and 23 lakes of different trophic status. Samples from some sites in the vicinity of the largest cities had significantly increased metal levels. In contrast, fish tissues from bog lakes had very low metal levels, possibly because of the high concentrations of natural organic matter in these waters.

Dynamics of metal availability and toxicity in historically polluted floodplain sediments.

Many floodplains contain high concentrations of sediment associated contaminants that might be subjected to large changes in terms of mobility, transformation and bioavailability. Therefore, this study describes 1) changes in the redox conditions and the mobility of metals in artificially uncovered polluted floodplain sediments, 2) metal uptake by organisms and 3) colonization, succession and functioning of benthic algae on these sediments. Flooding caused long term changes in redox potential (Eh) profiles. In top layers strong gradients in redox potential established quickly, while in deeper layers changes occurred more gradually. The availability of copper as measured by Diffusive Gradients in Thinfilms (DGT) showed a consistent relationship with fluctuations in Eh. However, this relationship was restricted to deeper layers in the sediment. Within 1 week high amounts of total copper were immobilized. Differences in total copper concentrations between polluted and clean sediments became only partially apparent when comparing the available copper fraction (DGT-Cu). Introduced Tubifex shows only marginal differences in levels of accumulated Cu. Colonization, growth and succession of algal communities on polluted sediments was not impaired, most likely due to low bioavailability. It is concluded that changing environmental conditions, such as flooding, can result in stable chemical conditions with low a availability of metals and hence in a diminution of actual ecological risks.

Tissue distribution and metabolism of benzo[a]pyrene in embryonic and larval medaka (Oryzias latipes).

The need to understand chemical uptake, distribution, and metabolism in embryonic and larval fish derives from the fact that these early life stages often exhibit greater sensitivity to xenobiotic compounds than do adult animals. In this study, a 6-h acute waterborne exposure immediately after fertilization was used to quickly load the egg with benzo[a]pyrene (BaP). This exposure was used to mimic the initial egg concentration of a persistent bioaccumulative toxicant that could result from maternal transfer. We used multiphoton laser scanning microscopy (MPLSM) in combination with conventional analytical chemistry methods to characterize the tissue distribution of BaP and its principal metabolites in medaka embryos and post-hatch larvae. Embryonic metabolism of BaP was evident by MPLSM prior to liver formation or heart development. A major product of this metabolism was identified by liquid chromatography/mass spectrometry as BaP-3-glucuronide. MPLSM showed that metabolites were sequestered within the yolk, biliary system, and gastrointestinal tract. When the gastrointestinal tract became patent a few days after hatch, the metabolites were rapidly eliminated. These findings indicate that some of the earliest embryonic tissues are metabolically competent and that redistribution of BaP and its metabolic products occurs throughout development. Rapid metabolism of BaP substantially reduces the body burden of parent chemical in the developing embryo, potentially reducing toxicity. It remains unclear whether metabolism of BaP in medaka embryos leads to the formation of DNA adducts associated with genotoxic effects or yields metabolites that later lead to other toxicity in juveniles or adults.

Effects of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) exposure on reproduction and hatchling development in Northern bobwhite quail.

Adult Northern bobwhite quail (Colinus virginianus) were exposed via food to octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), an energetic compound found in soils at military training installations. Depuration of HMX into eggs was examined in an initial study, and effects on egg production, hatching, growth, development, and survival of chicks were examined in a follow-up study. HMX was readily and rapidly transferred from female quail into eggs. Marked weight loss was observed in quail exposed to 125 and 250 mg/kg HMX in food, likely due to reductions in food intake rather than a toxic mechanism. In the second study, significant alterations in body mass occurred among quail at concentrations >52.5 +/- 9.3 mg/kg but not at 12.3 +/- 1.1 mg/kg in food. Treatment-related reductions in food consumption and decreases in egg laying rates were observed. No HMX-related effects were found in chick growth or survival. Quail inhabiting HMX-contaminated sites could possibly be exposed to HMX and therefore deposition of HMX into eggs is also possible. However, results of these studies further suggest that the potential for reproductive toxicity of HMX to birds is low.

In vitro analysis of the bioavailability of six metals via the gastro-intestinal tract of the rainbow trout (Oncorhynchus mykiss).

An in vitro gut sac technique was used to compare the uptake rates of essential (copper, zinc and nickel) and non-essential metals (silver, cadmium and lead) at 50 micromol L(-1) each (a typical nutritive level in solution in chyme) in the luminal saline in four sections of the gastro-intestinal tract (stomach, anterior, mid and posterior intestines) of the freshwater rainbow trout. Cu, Zn, Cd and Ag exhibited similar regional patterns: on an area-specific basis, uptake rates for these metals were highest in the anterior intestine, lowest in the stomach, and approximately equal in the mid and posterior intestinal segments. When these rates were converted to a whole animal basis, the predominance of the anterior intestine increased because of its greater area, while the contribution of the stomach rose slightly to approach those of the mid and posterior intestines. However, for Pb and Ni, area-specific and whole organism transport rates were greatest in the mid (Pb) and posterior (Ni) intestines. Surprisingly, total transport rates did not differ appreciably among the essential and non-essential metals, varying only from 0.025 (Ag) to 0.050 nmol g(-1)h(-1) (Ni), suggesting that a single rate constant can be applied for risk assessment purposes. These rates were generally comparable to previously reported uptake rates from waterborne exposures conducted at concentrations 1-4 orders of magnitude lower, indicating that both routes are likely important, and that gut transporters operate with much lower affinity than gill transporters. Except for Ni, more metal was bound to mucus and/or trapped in the mucosal epithelium than was transported into the blood space in every compartment except the anterior intestine, where net transport predominated. Overall, mucus binding was a significant predictor of net transport rate for every metal except Cd, and the strongest relationship was seen for Pb.

Two-stage removal of nitrate from groundwater using biological and chemical treatments.

In this study, we attempted to treat groundwater contaminated with nitrate using a two-stage removal system: one is biological treatment using the nitrate-degrading bacteria Pseudomonas sp. RS-7 and the other is chemical treatment using a coagulant. For the biological system, the effect of carbon sources on nitrate removal was first investigated using mineral salt medium (MSM) containing 500 mg l(-1) nitrate to select the most effective carbon source. Among three carbon sources, namely, glucose, starch and cellulose, starch at 1% was found to be the most effective. Thus, starch was used as a representative carbon source for the remaining part of the biological treatment where nitrate removal was carried out for MSM solution and groundwater samples containing 500 mg l(-1) and 460 mg l(-1) nitrate, respectively. About 86% and 89% of nitrate were removed from the MSM solution and groundwater samples, respectively at 72 h. Chemical coagulants such as alum, lime and poly aluminium chloride were tested for the removal of nitrate remaining in the samples. Among the coagulants, lime at 150 mg l(-1) exhibited the highest nitrate removal efficiency with complete disappearance for the MSM solutions. Thus, a combined system of biological and chemical treatments was found to be more effective for the complete removal of nitrate from groundwater.

Cadmium impact, accumulation and detection in poplar callus cells.

Effect of cadmium cations and their interaction with silicon cations was determined in poplar calli and expressed as changes in callus growth, cell viability and cadmium cation accumulation. Cell viability throughout culture versus cadmium cation accumulation in cells is discussed. At the same time, the study sought appropriate methods for cadmium cation detection in callus cells and also in experiments with low plant material (e.g. protoplasts). Cadmium cations were determined by atomic absorption spectroscopy and using fluorescence microscopy with a specific cadmium cation fluorescent dye. The detection of cadmium cations in callus cells by the latter method appears suitable because the callus cells are surrounded by primary cell walls without auto-fluorescence and these values fit well with atomic absorption spectroscopy quantification. However, the visualisation method has some limits discussed below.

Effects of sediment contamination on physiological and biochemical responses of the polychaete Diopatra neapolitana, an exploited natural resource.

The present study reports metal and arsenic contamination in sediments, as well as element accumulation and partitioning in the polychaete Diopatra neapolitana in the Ria de Aveiro lagoon (Portugal). The polychaetes biochemical performance and tissue regenerative capacity were also evaluated. The concentration of elements in sediments showed an increase of contamination among areas (areas A-G), but higher bioaccumulation was observed in organisms from a less contaminated area (area C, BAF>1). This study evidenced that individuals with higher elements bioaccumulation presented higher LPO and lower GSH/GSSG and also exhibited lower capacity for body regeneration. Polychaetes biotransformation capacity as well as antioxidant defense mechanisms were not sufficiently efficient to withstand the excess of ROS leading to increased LPO when organisms presented higher bioaccumulation levels. Additionally, an increase of methalotionines was also observed in individuals with higher bioaccumulation of metals and As, suggesting an induction of detoxification processes.

Ionic strength effect on copper biosorption by Sphaerotilus natans: equilibrium study and dynamic modelling in membrane reactor.

Biosorption of copper by Sphaerotilus natans in different conditions of ionic strength and pH was studied by performing sorption tests in batch and membrane reactors. Equilibrium batch tests evidenced the negative effect of ionic strength and the positive effect of pH on biosorption performances: the highest determined value for copper specific uptake, q, was about 60 mg/g at pH 6 and about 15 mg/g at pH 4. A competitive equilibrium model was successfully fitted to experimental data at different ionic strength levels to account for copper-sodium competition. In membrane reactor tests, experimental profiles of copper concentration in the permeate vs. time did not evidence a significant effect of ionic strength at low pH values (4 and 5). On the other hand a more remarkable effect of ionic strength on copper concentration in the permeate was observed at pH 6. Experimental profiles of continuous biosorption in the membrane reactors were successfully simulated by developing a dynamic model accounting for Cu-Na competition and for binding ability of cells fragments.

Distribution of micro-essential (Fe, Cu, Zn) and toxic (Hg) metals in tissues of two nutritionally distinct hydrothermal shrimps.

Hydrothermal ecosystems of the Mid Atlantic Ridge (MAR) are dominated by shrimps and mussels that are naturally exposed to elevated levels of heavy metals providing unique in situ laboratories for ecotoxicological investigations. This study reports on the tissue compartmentalization of both micro-essential (Fe, Zn, Cu) and toxic metals (Hg) in two nutritionally distinct cariddean vent shrimps: Rimicaris exoculata and Mirocaris fortunata, in order to shed light on organism-biota interactions at hydrothermal vents. High metal concentrations in shrimps confirmed extreme exposure levels at both geochemically different hydrothermal vents (Rainbow and Lucky Strike). However, Hg concentrations were below those reported in species for human consumption that may either suggest low bioavailability of the metal, or its effective detoxification/depuration by the hydrothermal shrimp that needs to be confirmed by post-capture toxicological investigations. Distribution of metals in different tissues had very similar patterns in both shrimp species, the target organs being gill and pylorus. Tissue levels correlated well with end-member fluid composition with regard to element ratios, i.e. Fe/Zn and Fe/Cu ratios in end-member fluids reported for Rainbow and L. Strike were conserved in the gills of M. fortunata. Moreover, R. exoculata that lives closer to venting exits as compared to M. fortunata, had similar or often less metals accumulated in selected organs, possibly owing to its higher degree of adaptation to hydrothermal conditions. Despite of high concentrations in tissues micro essential metals only represented a small fraction (14-36%) of the whole body burden indicating preponderance of minerals on the surface and/or in the gut, and thus points to improper use of whole body concentration in metal bioavailability interpretations at hydrothermal vents.

Gill reactivity of aluminium-species following liming.

In acidified aluminium (Al) rich freshwater positively charged Al-species (Al(i)) are the key toxic components due to the accumulation in fish gills. As a countermeasure, liming is used to increase the pH and reduce the concentration of Al(i)-species; in particular low molecular mass (LMM) Al(i)-species by hydrolyses. However, very toxic high molecular mass (HMM) Al polymers can form in the unstable mixing zone immediately after liming. In the present work gill reactivity of LMM and HMM Al-species was studied under controlled conditions in eight channel-tank mixing zone systems in the field where Atlantic salmon (Salmo salar L.) kept in cages were exposed to defined mixing zone water. Mixing zones were created by continually liming acid river water (pH 5.0-5.7) high in LMM Al(i) to pH 6.0 and 6.4, respectively. Transformation processes affecting the Al-speciation as a function of time after liming were documented by in situ hollow fibre ultrafiltration interfaced with ion chromatography, while the Al accumulation in fish gills was used as bioindicator. For fish exposed to mixing zone water immediately after liming (1 min) the Al accumulation in gills (mug Al g(-1)) was higher (factor of 2) than for fish exposed to acid water prior to liming, due to the formation of gill reactive HMM Al(i)-species. The Al accumulation in gills followed a first order kinetic expression reaching steady-state conditions after 24-h exposures. The deposition rate of Al in gills (mug Al g(-1) h(-1)) correlated with the water concentrations of HMM Al(i) (R(2)=0.80) in the mixing zones, and for LMM Al(i) in the acid water (R(2)=0.92). Due to the transient nature of HMM Al(i) the deposition rate of Al decreased from the point of liming with a factor of 10 downstream the channel-tank system (i.e. 100 min after liming). The concentration of gill accumulated Al was higher (factor of 3) immediately after high level liming (pH 6.4) than following low level liming (pH 6.0). However, high level liming was more efficient in detoxifying Al in downstream waters. Furthermore, the bioavailability of a given LMM Al(i) concentration as well as bioreactivity following liming was dependent on the TOC and silicon concentration in the acid water. Increased concentration of TOC (1.5 to 4.3 mg l(-1)) and silicon (0.3 to 1.0 mg l(-1)) reduced the gill reactivity of Al(i) by approximately 50%.