Bioaccumulation of aluminium in the freshwater snail Lymnaea stagnalis at neutral pH

Metabolism of the aquatic pollutant diclofenac in the Lymnaea stagnalis freshwater gastropod

The metabolism of organic contaminants in Lymnaea stagnalis freshwater gastropod remains unknown. Yet, pharmaceuticals-like the NSAID diclofenac-are continuously released in the aquatic environment, thereby representing a risk to aquatic organisms. In addition, lower invertebrates may be affected by this pollution since they are likely to bioaccumulate contaminants. The metabolism of pharmaceuticals in L. stagnalis requires further investigation to understand their detoxification mechanisms and characterized the risk posed by contaminant exposure in this species. In this study, a non-targeted strategy using liquid chromatography combined with high-resolution mass spectrometry was applied to highlight metabolites formed in L. stagnalis freshwater snails exposed to 300 µg/L diclofenac for 3 and 7 days. Nineteen metabolites were revealed by this approach, 12 of which were observed for the first time in an aquatic organism exposed to diclofenac. Phase I metabolism involved hydroxylation, with detection of 3'-, 4'-, and 5-hydroxydiclofenac and three dihydroxylated metabolites, as well as cyclization, oxidative decarboxylation, and dehydrogenation, while phase II metabolism consisted of glucose and sulfate conjugation. Among these reactions, the two main DCF detoxification pathways detected in L. stagnalis were hydroxylation (phase I) and glucosidation (phase II).

A workflow to investigate the impacts of weathered multi-walled carbon nanotubes to the mud snail Lymnaea stagnalis

Although the development and application of nanomaterials is a growing industry, little data is available on the ecotoxicological effects on aquatic organisms. Therefore, we set up a workflow to address the potential uptake of weathered multi-walled carbon nanotubes (wMWCNTs) by a model organism, the pulmonary mud snail Lymnaea stagnalis (L. stagnalis), which plays an important role in the food web. It represents a suitable organism for this approach because as a grazer it potentially ingests large amounts of sedimented wMWCNTs. As food source for L. stagnalis, benthic biofilm was investigated by the use of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) after exposure with wMWCNTs. In addition, isotopic labeling was applied with ¹⁴C-wMWCNTs (0.1 mg/L) to quantify fate, behavior, and enrichment of ¹⁴C-wMWCNTs in benthic biofilm and in L. stagnalis. Enrichment in benthic biofilm amounted to 529.0 µg wMWCNTs/g dry weight and in L. stagnalis to 79.6 µg wMWCNTs/g dry weight. A bioconcentration factor (BCF) for L. stagnalis was calculated (3500 L/kg). We demonstrate the accumulation of wMWCNTs (10 mg/L) in the digestive tract of L. stagnalis in an effect study. Moreover, the physiological markers glycogen and triglycerides as indicators for the physiological state, as well as the RNA/DNA ratio as growth indicator, were examined. No significant differences between exposed and control animals were analyzed for glycogen and triglycerides after 24 days of exposure, but a decreasing trend is recognizable for triglycerides. In contrast, the significant reduction in the RNA/DNA ratio of L. stagnalis indicated an inhibition of growth with a following recovery after depuration. The described workflow enables a comprehensive determination of the fate and the behavior of wMWCNTs specifically and in general all kinds of CNTs in the aquatic environment and therefore contributes to a holistic risk assessment of wMWCNTs.

Effect of Copper Sulphate (CuSO4) on Freshwater Snail, Physa acuta Draparnaud, 1805: A Histopathological Evaluation

In this study, freshwater snail (Physa acuta) was investigated to determine histopathological effects of CuSO₄ on digestive gland, foot, mantle and ovotestis under laboratory conditions. The snails were exposed to different sublethal concentrations of CuSO₄ (0.05 mg/L, 0.1 mg/L and 0.2 mg/L) periods of 10, 20 and 30 days. The relationship between CuSO₄ concentration and mortality rate in snails was calculated as Y = 8.8 + 125.14X, R² = 0.9444. The histopathological examinations revealed that CuSO₄ caused significant histopathological changes in all the tissues of the snail. The severity of these lesions in tissues increased with increasing CuSO₄ concentration and duration of exposure. The results showed that freshwater snail, Physa acuta can be considered to be a suitable bioindicator to demonstrate the toxic effect of copper in aquatic environments.

Exposure of earthworm (Eisenia fetida) to bauxite residue: Implications for future rehabilitation programmes

Bauxite residue is typically alkaline, has high sodium content and elevated concentrations of trace elements. Effective rehabilitation strategies are needed to mitigate potential environmental risks from its disposal and storage. Increasingly, the importance of viable soil faunal populations as well as establishment of vegetation covers is recognized as key components of successful rehabilitation. Inoculation with earthworms is a strategy for accelerating mine site rehabilitation, but little is known on the effects of bauxite residue properties on earthworm survival and viability. In the current study, earthworms (Eisenia fetida) were exposed for 28 days to a series of bauxite residue/soil treatments (0, 10, 25, 35, 50, 75 and 100% residue) to evaluate possible toxic effects on earthworms, investigate the bioavailability of relevant elements (e.g. As, Cr, V), and assess the risk of element transfer. Results showed that soil containing ≥25% residue (pH ≥ 9.8; ESP ≥ 18.5%; extractable Na ≥ 1122 mg/kg) significantly impacted survival (mortality ≥28%) and reproduction (cocoon production inhibition ≥76%) of the exposed earthworms. Alkalinity, sodicity and bioavailable Na were identified as major factors causing toxicity and some earthworms were observed to adopt compensative response (i.e. swollen body) to cope with osmotic stress. Conversely, soil containing 10% residue (pH = 9.1; ESP = 9.2%; extractable Na = 472 mg/kg) did not elicit significant toxicity at the organism level, but biomarker analysis (i.e. superoxide dismutase and catalase) in earthworm coelomocytes showed an oxidative stress. Furthermore, earthworms exposed to soil containing ≥10% residue took up and accumulated elevated concentrations of Al, As, Cr and V in comparison to the control earthworms. We concluded that earthworm inoculation could be used in future rehabilitation programmes once the key parameters responsible for toxicity are lowered below specific target values (i.e. pH = 9.1, ESP = 18.5%, extractable Na = 1122 mg/kg for Eisenia fetida). Nonetheless, trace element uptake in earthworms should be regularly monitored and the risk to the food chain further investigated.

Lymnaea stagnalis as a freshwater model invertebrate for ecotoxicological studies

Lymnaea stagnalis, also referred to as great or common pond snail, is an abundant and widespread invertebrate species colonizing temperate limnic systems. Given the species importance, studies involving L. stagnalis have the potential to produce scientifically relevant information, leading to a better understanding of the damage caused by aquatic contamination, as well as the modes of action of toxicants. Lymnaea stagnalis individuals are easily maintained in laboratory conditions, with a lifespan of about two years. The snails are hermaphrodites and sexual maturity occurs about three months after egg laying. Importantly, they can produce a high number of offspring all year round and are considered well suited for use in investigations targeting the identification of developmental and reproductive impairments. The primary aims of this review were two-fold: i) to provide an updated and insightful compilation of established toxicological measures determined in both chronic and acute toxicity assays, as useful tool to the design and development of future research; and ii) to provide a state of the art related to direct toxicant exposure and its potentially negative effects on this species. Relevant and informative studies were analysed and discussed. Knowledge gaps in need to be addressed in the near future were further identified.

Different responses of abalone Haliotis discus hannai to waterborne and dietary-borne copper and zincexposure

To investigate the potential influence of the contamination of copper (Cu) or zinc (Zn), the abalone Haliotis discus hannai was exposed to waterborne or macroalgae-borne Cu or Zn over a period of 8weeks. Both Cu and Zn were effectively accumulated by the abalones from water or macroalgae, but their concentration factors and trophic transfer factors were low due to the regulation of Cu and Zn accumulation. Following waterborne or dietary exposure, the abalones exhibited different accumulation patterns of Cu and Zn. The tissue Zn burden decreased quickly after the initial accumulation, and the incoming Zn was mainly deposited in the viscera. In contrast, the tissue Cu burden increased rapidly and gradually reached a steady state. The abalone muscle exhibited a comparable storage capacity of Cu as the viscera and the accumulated Cu in muscle was mainly derived from the dissolved phase instead of trophic transfer. The feeding and growth of the abalone were not influenced in all the exposure regimes. Moreover, the significant induction of metallothionein indicated that the bioaccumulated metals were actively detoxified. In the metal-exposed abalones, more Cu was distributed into the biologically detoxified fractions (metallothionein-like protein and/or metal-rich granule), whereas no significant subcellular redistribution of Zn was observed. Our study suggested that the abalone may have high endurance to the contamination of Cuor Zn.

Toxicity of aluminium in natural waters controlled by type rather than quantity of natural organic matter

Extension of the conditions under which Al toxicity is tested is required. Environmentally representative preparation of waters is used in investigating roles of alginate (AA) and humic acids (HA) in partitioning of Al (0.5 mg L(-1)), subsequent uptake and accumulation by and toxicity to Lymnaea stagnalis. HA and AA did not alter precipitation of Al(OH)3, but altered subsequent behaviour of Al. High (40 mg L(-1)) HA concentrations, and to a lesser extent AA, prevented settling and availability for benthic grazing but made deposited Al more likely to be ingested. HA detoxified but AA increased toxicity relative to Al alone. Low concentration (4 mg L(-1)) AA and HA do not change partitioning but increase uptake; they both detoxify, but AA less than HA. The study shows OC:Al ratio is critical in predicting Al behaviour in natural waters, also uptake is mediated by snail behaviour, not solely a function of concentration and form of Al. Therefore, predicting Al behaviour will be subject to errors in determining relevant water composition and response of biota to the new speciation. However, with respect to toxicity, rather than other aspects of Al behaviour, different ratios of HA and Al are insignificant compared to whether AA is present rather than HA.

Metal/metalloid accumulation/remobilization during aquatic litter decomposition in freshwater: a review

The focus of this article is to combine two main areas of research activities in freshwater ecosystems: the effect of inorganic pollutants on freshwater ecosystems and litter decomposition as a fundamental ecological process in streams. The decomposition of plant litter in aquatic systems as a main energy source in running water ecosystems proceeds in three distinct temporal stages of leaching, conditioning and fragmentation. During these stages metals and metalloids may be fixed by litter, its decay products and the associated organisms. The global-scale problem of contaminated freshwater ecosystems by metals and metalloids has led to many investigations on the acute and chronic toxicity of these elements to plants and animals as well as the impact on animal activity under laboratory conditions. Where sorption properties and accumulation/remobilization potential of metals in sediments and attached microorganisms are quite well understood, the combination of both research areas concerning the impact of higher trophic levels on the modification of sediment sorption conditions and the influence of metal/metalloid pollution on decomposition of plant litter mediated by decomposer community, as well as the effect of high metal load during litter decay on organism health under field conditions, has still to be elucidated. So far it was found that microbes and invertebrate shredder (species of the genera Gammarus and Asellus) have a significant influence on metal fixation on litter. Not many studies focus on the impact of other functional groups affecting litter decay (e.g. grazer and collectors) or other main processes in freshwater ecosystems like bioturbation (e.g. Tubifex, Chironomus) on metal fixation/release.

Accumulation and toxicity of aluminium-contaminated food in the freshwater crayfish, Pacifastacus leniusculus

The accumulation and toxicity of aluminium in freshwater organisms have primarily been examined following aqueous exposure. This study investigated the uptake, excretion and toxicity of aluminium when presented as aluminium-contaminated food. Adult Pacifastacus leniusculus were fed control (3 μg aluminium/g) or aluminium-spiked pellets (420 μg aluminium/g) over 28 days. Half the crayfish in each group were then killed and the remainder fed control pellets for a further 10 days (clearance period). Concentrations of aluminium plus the essential metals calcium, copper, potassium and sodium were measured in the gill, hepatopancreas, flexor muscle, antennal gland (kidney) and haemolymph. Histopathological analysis of tissue damage and sub-cellular distribution of aluminium were examined in the hepatopancreas. Haemocyte number and protein concentration in the haemolymph were analysed as indicators of toxicity. The hepatopancreas of aluminium-fed crayfish contained significantly more aluminium than controls on days 28 and 38, and this amount was positively correlated with the amount ingested. More than 50% of the aluminium in the hepatopancreas of aluminium-fed crayfish was located in sub-cellular fractions thought to be involved in metal detoxification. Aluminium concentrations were also high in the antennal glands of aluminium-fed crayfish suggesting that some of the aluminium lost from the hepatopancreas is excreted. Aluminium exposure via contaminated food caused inflammation in the hepatopancreas but did not affect the number of circulating haemocytes, haemolymph ion concentrations or protein levels. In conclusion, crayfish accumulate, store and excrete aluminium from contaminated food with only localised toxicity.

Trophic transfer of aluminium through an aquatic grazer-omnivore food chain

The potential for trophic transfer of aluminium (Al) was investigated using a grazing detritivore, the freshwater snail Lymnaea stagnalis, and a predator, the signal crayfish Pacifastacus leniusculus. Snails were exposed to either aqueous Al (500 microg l(-1)) in the presence or absence of an inorganic ligand (phosphate (+P); 500 microg l(-1)) for 30 days, or kept as unexposed controls. Subcellular partitioning of Al in the snail tissues was characterised using ultracentrifugation. Al content in the soft tissues and the subcellular fractions was measured using inductively coupled plasma atomic emission spectroscopy. Exposed and control snails were fed to individually housed crayfish (n=6 per group) over 40 days. Water samples, uneaten snail tissue and faeces were collected throughout the experiment in order to assess the fate of Al. Behavioural toxicity to the crayfish was assessed at four time points, and tissue accumulation of Al in soft tissues was measured following a 2-day depuration period. Snails exposed to Al+P accumulated more Al per snail than those exposed to Al only (291 microg vs 206 microg), and also contained a higher proportion of detoxified Al (in inorganic granules and associated with heat stable proteins) (39% vs 26%). There were no significant differences in behavioural activity between the different groups of crayfish at any time point. Crayfish fed snails exposed to only Al accumulated significant levels of Al in their total soft tissues, compared to controls; crayfish fed Al+P-exposed snails did not, even though concentrations of Al in these snails were higher. The highest concentrations of Al were found in the green gland in both crayfish feeding groups, and the gut and hepatopancreas in crayfish fed Al only exposed snails; all of these were significantly higher than in crayfish fed control snails. There was no significant accumulation of Al in the gills or flexor muscle in any group. At least 17% of trophically available Al in the snail tissues was accumulated by the crayfish. This proportion was similar in both feeding groups but, as the proportion of trophically available Al in the snails exposed to Al+P was lower, this led to lower accumulation in the Al+P crayfish feeding group. This study indicates that in comparison to vertebrates, aquatic invertebrates accumulate a higher proportion of Al via oral ingestion but it does not accumulate in tissues that may pose a threat to human consumers.

Tissue accumulation of aluminium is not a predictor of toxicity in the freshwater snail, Lymnaea stagnalis

The amount of toxic metal accumulated by an organism is often taken as an indicator of potential toxicity. We investigated this relationship in the freshwater snail, Lymnaea stagnalis, exposed to 500 microg l(-1) Al over 30 days, either alone or in the presence of phosphate (500 microg l(-1) P) or a fulvic acid surrogate (FAS; 10 mg l(-1) C). Behavioural activity was assessed and tissue accumulation of Al quantified. Lability of Al within the water column was a good predictor of toxicity. FAS increased both Al lability and behavioural dysfunction, whereas phosphate reduced Al lability, and completely abolished Al-induced behavioural toxicity. Tissue accumulation of Al was not linked to toxicity. Higher levels of Al were accumulated in snails exposed to Al + P, compared to those exposed to Al alone, whereas FAS reduced Al accumulation. These findings demonstrate that the degree of tissue accumulation of a metal can be independent of toxicity.

Avoidance of aluminum toxicity in freshwater snails involves intracellular silicon-aluminum biointeraction

Silicon (Si) ameliorates aluminum (Al) toxicity to a range of organisms, but in almost all cases this is due to ex vivo Si-Al interactions forming inert hydroxyaluminosilicates (HAS). We hypothesized a Si-specific intracellular mechanism for Al detoxification in aquatic snails, involving regulation of orthosilicic acid [Si(OH)4]. However, the possibility of ex vivo formation and uptake of soluble HAS could not be ruled out Here we provide unequivocal evidence for Si-Al interaction in vivo, including their intracellular colocalization. In snails preloaded with Si(0H)4, behavioral toxicity in response to subsequent exposure to Al was abolished. Similarly, recovery from Al-induced toxicity was faster when Si(OH)4 was provided, together with rapid loss of Al from the major detoxificatory organ (digestive gland). Temporal separation of Al and Si exposure excluded the possibility of their interaction ex vivo. Elemental mapping using analytical transmission electron microscopy revealed nanometre-scale colocalization of Si and Al within excretory granules in the digestive gland, consistent with recruitment of Si(OH)4, followed by high-affinity Al binding to form particles similarto allophane, an amorphous HAS. Given the environmental abundance of both elements, we anticipate this to be a widespread phenomenon, providing a cellular defense against the profoundly toxic Al(III) ion.

Effects of freshly neutralized aluminum on oxygen consumption by freshwater invertebrates

The hypothesis tested in this study was if a pulse of precipitating aluminum (Al) at circumneutral pH covers the body of an invertebrate and, therefore, reduces the surface area available for respiration, organisms exposed to precipitating Al in an experimental system should consume less oxygen than organisms not exposed to aluminum. To test this hypothesis, experiments were conducted in the laboratory placing test organisms in biochemical oxygen demand (BOD) bottles containing a recently neutralized acidic, Al-enriched solution; conditions were meant to loosely mimic those of an acidic, Al-rich stream flowing into a larger, neutralizing receiving stream. The experiments suggested that freshly neutralized Al, i.e., Al in transition from ionic species in acidic waters to polymers or precipitating hydroxides after a rapid increase to pH > or = 6.8, impaired oxygen consumption by D. magna in a repeatable, dose-dependent fashion. Precipitating Al also impaired oxygen consumption by the perlid stoneflies Perlesta lagoi and Acroneuria abnormis, at the lower concentrations used, but higher concentrations resulted in oxygen consumption similar to that of controls. An ionoregulatory impairment response may explain this trend. Aluminum did not affect oxygen consumption by the larger, detritivorous stonefly, Pteronarcys pictetii.

Effect of humic acid on water chemistry, bioavailability and toxicity of aluminium in the freshwater snail, Lymnaea stagnalis, at neutral pH

The influence of humic acid on the water chemistry of environmentally relevant concentrations of Al at neutral pH was studied, together with its effect on the bioavailability and toxicity of Al in Lymnaea stagnalis. Humic acid significantly reduced the loss of Al from the water and increased the fraction of filterable Al, although this was a relatively small fraction of total Al. Filterable Al concentration in the presence or absence of humic acid was independent of initial Al concentration. Humic acid only partly reduced toxicity, as observed by a reduction in behavioural suppression, and had no effect on the level of Al accumulated in tissues. These results suggest that humic acid maintains Al in a colloidal form that is bioavailable to L. stagnalis. However, these colloidal Al-humic acid species were less toxic since behavioural toxicity was reduced. Humic acid may play an important role in limiting the toxicity of Al to freshwater organisms.

Toxic effects of Al-based coagulants on Brassica chinensis and Raphanus sativus growing in acid and neutral conditions

The ecotoxicological effects of aluminum (Al)-based coagulants are of concern because of their wide-ranging applications in wastewater treatment and water purification. As important Al-based coagulants, AlCl(3) and PAC (polyaluminum-chloride) were selected as examples to examine the toxic effects on representative vegetables including the cabbage Brassica chinensis and the radish Raphanus sativus over a range of exposure concentrations in neutral (pH 7.00) and acidic (pH 4.00) conditions, using seed germination and root elongation in the early-growth stage as indicators of toxicity. The results showed that root elongation of the two vegetables was a more sensitive indicator than was seed germination for evaluating the toxicity of Al. As a single influencing factor, H(+) had no significant direct effects on root elongation of Brassica chinensis and Raphanus sativus under the experimental conditions. The toxicity of Al played the main role in inhibiting root elongation and seed germination and was strongly related to changes in pH. There was a markedly positive relationship between the inhibitory rate of root elongation, seed germination, and the concentration of Al at pH 4.00 (p < 0.01). The toxic effect of AlCl(3) on Brassica chinensis was less with a neutral pH than at pH 4.00, but Raphanus sativus was more susceptible to AlCl(3) toxicity at a neutral pH than at pH 4.00. Both Raphanus sativus and Brassica chinensis had a more toxic response to a low concentration (<64 mg . L(-1)) of PAC in a neutral condition than in an acidic condition. Undoubtedly, the Al toxicity caused by Al-based coagulants at a neutral pH is relevant when treatment solids are used in agriculture.

Role of exogenous and endogenous silicon in ameliorating behavioural responses to aluminium in a freshwater snail

Aluminium accumulation by the freshwater snail Lymnaea stagnalis is correlated with behavioural depression which is ameliorated by addition of orthosilicic acid. We hypothesised that Si is relocated to the digestive gland in response to Al, leading to the formation of non-toxic hydroxyaluminosilicates (HAS). Exposure to 500 microg l(-1) Al for 30 days was associated with an initial period of behavioural depression, followed by apparent tolerance and subsequent depression, suggesting saturation of the cellular detoxification pathway during prolonged exposure. Exogenous Si (7.77 mg l(-1)) completely ameliorated all behavioural effects of Al but did not prevent its accumulation. In the presence of added Al, significantly more of this Si was accumulated by the tissues, compared to controls and snails exposed to Si alone. In snails exposed to Al plus Si, Al and Si concentrations were significantly correlated, with a ratio around 3:1 Al:Si, consistent with the presence of the non-toxic HAS protoimogolite.

Effect of orthosilicic acid on the accumulation of trace metals by the pond snail Lymnaea stagnalis

Silicon (Si) has a marked affinity for aluminium (Al(III)), but not other trace metals such as cadmium (Cd(II)) and zinc (Zn(II)). Exogenous orthosilicic acid (Si(OH)(4)) ameliorates the toxicity of Al(III) to the pond snail Lymnaea stagnalis, but its mechanism of action is unclear. Here, studies were conducted to ascertain whether interaction between orthosilicic acid and Al(III) occurs in the water column to prevent Al(III) uptake, or in the tissues to reduce the toxicity of accumulated metal. Silicon did not reduce the accumulation of Al(III) by the digestive gland (the main "sink" for trace metals in L. stagnalis) following exposure of the snail for 30 days to 500 microg l(-1) added Al(III) and 13-fold molar excess of orthosilicic acid. However, Si concentrations correlated well with Al(III) levels in the digestive gland (R(2)=0.77), giving a ratio of 2.5:1 (Al(III):Si). Exposure to Zn(II) or Cd(II) and 13-fold molar excess of orthosilicic acid did not prevent uptake of these metals, or result in a correlation between metal and Si concentrations of the snail digestive gland. These data show that aquated orthosilicic acid does not prevent Al(III) accumulation by L. stagnalis. However, following exposure, the ratio of Al(III) to Si in the digestive gland is suggestive of the early formation of hydroxyaluminosilicates, probably proto-imogolites (2-3:1 Al(III):Si). Whether hydroxyaluminates are formed ex vivo in the water column and taken up by snails into the digestive gland, or formed in situ within the digestive gland remains to be established. Either way, orthosilicic acid clearly prevents the in vivo toxicity of Al(III) rather than reducing its uptake. Silicon appears to have an important role in the handling Al(III) by the pond snail which may also have wider relevance in understanding the role of Si in ameliorating Al(III) toxicity.

Effect of sub-lethal concentrations of aluminium on the filtration activity of the freshwater mussel Anodonta cygnea L. at neutral pH

Significant amounts of aluminium (Al) are commonly present in rivers and lakes, largely in particulate form in neutral waters. Freshwater bivalves, as filter feeders are therefore exposed to both particulate and dissolved metal and are potentially vulnerable to Al. The effect of Al on filtering behaviour of the freshwater mussel Anodonta cygnea L. was investigated during short (1 hour) and long-term (15 days) exposure to environmentally relevant concentrations (250 and 500 microg l(-1)) at neutral pH. Water flow through the outflow siphon was monitored as an indicator of pumping capacity. Short-term (1 hour) exposure to 500 microg l(-1) added Al produced an irreversible decrease in the duration of filtering periods, presumably as an avoidance response to the toxicant. One-hour exposure 250 microg l(-1) Al had no detectable effect. When mussels were exposed to 250 or 500 microg l(-1) added Al for 15 days, siphon activity measured in days 11-15 of exposure was inhibited by 50% and 65%, respectively, compared to pre-exposure levels. Recovery occurred following transfer of mussels to uncontaminated water. Interaction between Al and freshwater bivalves at neutral pH may affect both the performance of the mussels and the chemical speciation of the metal in the natural environment.

Functional and structural rearrangements of salivary gland polytene chromosomes of Chironomus riparius Mg. (Diptera,Chironomidae) in response to freshly neutralized aluminium

Although recent work has shown that environmentally relevant concentrations of freshly neutralized aluminium (AI) are bioavailable and toxic to freshwater invertebrates, the genotoxicity of Al has not been examined. Here we show that freshly neutralized Al affects structure and function of the salivary gland polytene chromosomes of the ubiquitous chironomid larva Chironomus riparius over three generations. Exposure to 500 microg l-1 added Al for 24-25 days resulted in a significantly higher frequency of numerous somatic aberrations, while no structural aberrations were found in F1 controls and few in the second and third generation. Aberrations also included deletions of sections of chromosome G of C. riparius larvae as well as deletions of one or more Balbiani rings. Changes in functional activity included decreased activity of the Balbiani rings (BR), and an increase in the number of decondensed centromeres. The activity of the nucleolar organizer (NOR) significantly decreased in F1 chironomids exposed to Al, while in the F2 and F3 generations the NOR showed normal (high) activity. First generation chironomids were generally more susceptible to Al although no clear evidence of tolerance was apparent over three generations. The possible use of alterations in chironomid polytene chromosomes as biomarkers of trace metal pollution is discussed.

Influence of oligomeric silicic and humic acids on aluminum accumulation in a freshwater grazing invertebrate

This study examined the influence of oligomeric silicic acid and humic acid on aluminum in the water column and its accumulation in the freshwater snail Lymnaea stagnalis. Forty-eight hours after addition of Al (500 microg L(-1)), 83% of the metal was lost from the water column. This loss was reduced by oligomeric silica (20 mg L(-1)) and by humic acid (10 mg L(-1)). Aluminum accumulated in the digestive gland and, to a lesser extent, in the remaining soft tissues, and this accumulation was reduced by oligomeric silica. In the presence of humic acid, Al accumulation in the digestive gland was unaffected, though less was accumulated in the remaining tissues. Snails accumulated Si preferentially in the digestive gland and this accumulation was increased in the presence of added Al. Thus, both oligomeric silica and humic acid influence Al bioavailability and Si is upregulated in the digestive gland in the presence of Al.

Interaction of mucus with freshly neutralised aluminium in freshwater

This study examined the interaction of mollusc trail mucus, and its biochemical constituents, with environmentally relevant concentrations of freshly neutralised aluminium (Al) in freshwater. Upon neutralisation Al starts to polymerise. In the presence of mucus the metal is rapidly localised into the hydrated mucus gel resulting in a likely reduction of its overall degree of polymerisation. A simple Al binding assay identified large-M(r) glycoconjugates as major Al-complexing molecules in mucus. Subsequent isolation and purification of these mucus glycoconjugates showed the metal readily bound to the carbohydrate portion and, in particular, to acidic components such as those containing carboxyl functionality. It is suggested gel-forming extracellular glycoconjugates play a crucial role in preventing the diffusion of Al into biological systems and thus serve to maintain metabolic homeostasis.

Aluminum-dependent regulation of intracellular silicon in the aquatic invertebrate Lymnaea stagnalis

Silicon is essential for some plants, diatoms, and sponges but, in higher animals, its endogenous regulation has not been demonstrated. Silicate ions may be natural ligands for aluminum and here we show that, in the freshwater snail (Lymnaea stagnalis), intracellular silicon seems specifically up-regulated in response to sublethal aluminum exposure. X-ray microanalysis showed that exposure of snails to low levels of aluminum led to its accumulation in lysosomal granules, accompanied by marked up-regulation of silicon. Increased lysosomal levels of silicon were a specific response to aluminum because cadmium and zinc had no such effect. Furthermore, intra-lysosomal sulfur from metallothionein and other sulfur-containing ligands was increased after exposure to cadmium and zinc but not aluminum. To ensure that these findings indicated a specific in vivo response, and not ex vivo formation of hydroxy-aluminosilicates (HAS) from added aluminum (555 microg/liter) and water-borne silicon (43 microg/liter), two further studies were undertaken. In a ligand competition assay the lability of aluminum (527 microg/liter) was completely unaffected by the presence of silicon (46 microg/liter), suggesting the absence of HAS. In addition, exogenous silicon (6.5 mg/liter), added to the water column to promote formation of HAS, caused a decrease in lysosomal aluminum accumulation, showing that uptake of HAS would not explain the loading of aluminum into lysosomal granules. These findings, and arguments on the stability, lability, and kinetics of aluminum-silicate interactions, suggest that a silicon-specific mechanism exists for the in vivo detoxification of aluminum, which provides regulatory evidence of silicon in a multicellular organism.

Avoidance responses to aluminium in the freshwater bivalve Anodonta cygnea

This study examined the effect of aluminium (Al) on the filtering behaviour (shell opening or gape) of the freshwater bivalve Anodonta cygnea L in neutral fresh water. Parallel measurements of Al concentration in the soft tissues were made to examine the relationship between changes in behaviour and accumulation of Al. The number of lysosomal granules in the gill, kidney and digestive gland were counted, as lysosomes are known to be involved in the excretion and detoxification of trace metals. The bivalves were exposed to two environmentally relevant concentrations of added Al i.e. 250 and 500 microg l(-1) (9.25 and 18.5 microM l(-1)) at neutral pH for 15 days and shell movement monitored continuously. Aluminium affected the mussels' filtering activity, producing an avoidance reaction whose magnitude was concentration-dependent; 250 microg l(-1) added Al produced no detectable change, while 500 microg l(-1) Al reduced mean duration of shell opening by 50%. This effect was irreversible over a 15 day recovery period. Tissue levels of Al after 15 days exposure were an order of magnitude higher in animals exposed to 250 microg l(-1) added Al than in those exposed to 500 microg l(-1). This was consistent with the inhibition of filtering activity due to valve closure at the higher concentration, which may have prevented uptake of Al. In addition, probable different chemical speciation of Al in the water column (soluble for 250 and colloidal for 500 microg l(-1)) may lead to marked differences in tissue uptake. The kidney and digestive gland were the main sites of accumulation of Al and concentrations remained significantly elevated 15 days after transfer of animals to clean water. It is suggested that mucus plays a role in the exclusion of Al as elevated concentrations were measured in the pseudofaeces of animals during and after exposure. Lysosomal granules may be involved in the intracellular handling and detoxification of Al as numbers increased significantly in all organs during exposure and continued to increase after the animals were transferred to clean water. The present study provides evidence for the bioavailability and toxicity of Al to mussels at neutral pH and at concentrations which are known to enter neutral freshwaters when mobilised by natural or anthropogenic acidity. The changes in behaviour and uptake of Al in the mussel observed in this investigation are, therefore, likely to be reflected in the natural environment and the degree to which Al affects the 'fitness' of the mussel populations and the transfer of Al through the food chain merit investigation.

Winter third- to fourth-instar larvae of Chironomus plumosus as bioassay tools for assessment of acute toxicity of metals and their binary combinations

The ecotoxicological effect expressed as mortality of four metal ions (Cd, Cu, Zn, Al) and their associations on winter third- to fourth-instar larvae of Chironomus plumosus was determined. The effect of individual metals was introduced as acute toxicological effect and expressed as LC(50) and LC95 values with 95% intervals of confidence. On the basis of the LC50 values the toxicity of metals after 96 h treatment was ranked Cu>>Cd>Zn>Al. Copper was at least 100 times more toxic than other metals tested. When the acute toxic effect of metal pairs was observed, in general, deleterious effects were directly proportional to metal concentrations. The toxicity of metals in combinations was different from that of individual metals, because of either antagonism or synergism. From the results obtained it can be concluded that when in metal pairs in which the original metal (the metal for which the interaction was determined) is at the lower concentration (Cd 10 mg x L(-1), Zn 25 mg x L(-1), Al 25 mg x L(-1), Cu 0.1 mg x L(-1)), the prevailing interaction is synergism (mortality was higher for metal combinations than for individual metals). Except for an overadditive effect (synergism), additivity was also confirmed in some cases (Al25+Cd10; Al25+Cd25; Al25+Cu0.1; Cu0.1+Cd10; Cu0.1+Cd25; Cu0.1+Al50). Synergism, in combinations in which the original metal is at the higher concentration (Cd 25 mg x L(-1), Zn 50 mg x L(-1), Al 50 mg x L(-1), Cu 1.0 mg x L(-1)), was observed only for the pairs Zn50+Al25 and Zn50+Cu1.0. Reciprocal additivity was observed after 96 h of treatment only for the combination Zn50+Al50. For all other binary combinations in which the original metal was at the higher concentration, an antagonistic effect was confirmed.

Localization and fate of aluminium in the digestive gland of the freshwater snail Lymnaea stagnalis

The digestive gland of the freshwater snail Lymnaea stagnalis, exposed to water containing an elevated concentration of aluminium at neutral pH for up to 30 days, followed by a 20 day recovery period, was examined by light and electron microscopy and X-ray microanalysis. Aluminium was localized in the yellow granules present in the digestive and excretory cells and in the green and small granules present in the digestive cells. More aluminium, silicon, phosphorus and sulphur were present in all three granule types from aluminium exposed snails. The number of yellow and green granules from the digestive gland of aluminium exposed snails showed a progressive increase over the experimental period compared to controls. The number and aluminium content of the granules is likely to reflect the role of the digestive gland as a 'sink' for accumulated aluminium. We propose that intracellular monomeric silica is involved in the detoxification of aqueous aluminium which at neutral pH is largely in the form of an insoluble polyhydroxide. The increased amounts of sulphur and phosphorus in the granules are likely to be part of a broad response to metal loading but probably do not play a significant role in the storage and detoxification of aluminium.

Accumulation of aluminium by the freshwater crustacean Asellus aquaticus in neutral water

This study examined the accumulation of aluminium (Al), mostly as the insoluble (Al(OH)(3)) species, by the freshwater crustacean Asellus aquaticus at neutral pH. Animals were exposed to a range of Al concentrations (5-356 microg l(-1)) in three experiments. The first two were of 30 and 50 days duration, respectively, followed by transfer of the A. aquaticus to water containing no Al for 20 days. The third used live and dead animals in order to investigate the contribution made by surface adsorption of Al to the total accumulated. Significant accumulation of Al in the whole tissues occurred by day 10 in all animals in the 30- and 50- day experiment. Peak concentrations of Al were measured in animals between days 10 and 20 with high concentration factors ranging from 1.4 x 10(4) to 5.5 x 10(3). By day 30, accumulated Al had fallen but was still significantly greater than the control in the 50- day exposure experiment. This 30- day increase followed by decreased accumulation of Al was repeated over the remaining exposure period (i.e. 30-50 days) although rates of uptake and loss and peak tissue levels of Al were higher. Proportionality between environmental (water) and tissue concentrations of Al occurred at day 20 but not at day 45. Significantly more Al was accumulated by dead animals than live animals at all Al exposure concentrations. These results suggest that Al is available to the crustacean at neutral pH and that the cuticle may provide an important site of uptake.