The effect of salinity on cadmium toxicity to the estuarine mysid Mysidopsis bahia: role of chemical speciation

The effect of salinity on the toxicity of cadmium to the bay mysid, Mysidopsis bahia Molenock, was studied. When toxicity was expressed in terms of free cadmium ion (Cd²⁺) rather than total cadmium (Cd_T), CdCl⁺ or CdCl₂ only a slight salinity effect was apparent, suggesting that Cd²⁺ is the primary toxic species. Mysids were more tolerant of Cd²⁺ at an intermediate salinity of 22‰ and less tolerant at low and high salinity extremes (6 and 38‰). Alteration of cadmium speciation by use of an artificial ligand, nitrilotriacetic acid (NTA), over a range of salinities (14–34‰) produced conflicting results. Toxicity of Cd²⁺ was independent of Cd_T concentration at a given salinity but increased with increasing salinity and/or NTA concentration and was determined to be the result of salinity—Cd²⁺ and NTA-Cd²⁺ interactions. Possible mechanisms of the salinity effect and NTA interaction with cadmium toxicity are discussed.     

Impairment of mysid (Neomysis integer) swimming ability: an environmentally realistic assessment of the impact of cadmium exposure

Neomysis integer (Crustacea: Mysidacea), a euryhaline member of the hyperbenthos of the upper reaches of European estuaries, has been identified as a suitable animal for assessing the impacts of chemical pollutants on these estuarine regions. In this study, the effect of a 7 day pre-exposure to environmentally relevant concentrations of cadmium (0.5 and 1.0 microg l(-1)) on the swimming behaviour of N. integer was examined using an annular flume. Cadmium speciation at two salinities (1 and 10 per thousand) that dominate these upper estuarine regions was modelled to ensure mysids were exposed to the same concentration of the toxic free-ion at each salinity. There was no significant difference in the swimming behaviour of mysids exposed to the same free-ion cadmium concentration at the two different salinities. At each salinity, exposure to 0.5 microg Cd2+ (aq) l(-1)resulted in fewer mysids moving forward into the current (normal behaviour) at free stream velocities typical of their natural habitat (e.g. 3-9 cm s(-1)) than non cadmium-exposed mysids. At these low current speeds, cadmium-exposed mysids were either able to maintain position or were swept by the current. The same general responses were recorded for mysids exposed to 1.0 microg Cd2+ (aq) l(-1)except that more mysids showed disrupted swimming ability compared with 0.5 microg Cd2+ (aq) l(-1). At higher current speeds (>12 cm s(-1)), current velocity was the dominant factor affecting mysid swimming behaviour and there was no effect of cadmium on mysids maintaining position. Exposure to cadmium also caused significant disruption of the hyperbenthic behaviour of N. integer and more cadmium-exposed individuals were in the water column than control mysids; this result was more variable at 10 per thousand than 1 per thousand. Results indicate that exposure to cadmium concentrations of 0.5 microg Cd2+(aq) l(-1)would result in displacement of N. integer from its optimum region within the estuarine environment. This conclusion would not be achieved from standard LC(50) tests (e.g. 7 day LC50 = 2.95 microg Cd2+ (aq) l(-1)), highlighting the value of behavioural disruption as a sensitive indicator of environmental chemical contamination.     

Influence of salinity on metal toxicity to Ulva pertusa

The present study was undertaken to establish the effect of salinity on the toxicity of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) to Ulva pertusa, with inhibition of spore release used as the endpoint. The optimal salinity for maximal spore release for U. pertusa was found to be between 20 and 40 psu. Comparisons between toxicity of metals, as measured by EC₅₀, was shown to be in the descending order of Cu>Cd>Pb=Zn, which is similar to the toxicity of metals to algae, in general. When salinity was decreased from 30 to 20 psu, the EC₅₀ values for Cd toxicity to the inhibition of spore release in U. pertusa decreased from 261 to 103 g·L^?1, whereas increased salinity from 30 to 40 psu increased the EC₅₀ from 261 to 801 g·L^?1. Similarly, EC₅₀ values for Cu toxicity were 52 g·L^?1 at 20 psu, 99 g·L^?1 at 30 psu, and 225 g·L^?1 at 40 psu, and for Zn toxicity were 720 g·L^?1, 1,074 g·L^?1 and 1,520 g·L^?1, at 20, 30 and 40 psu, respectively. In contrast, no salinity dependent change in EC₅₀ values was apparent for Pb, with no significant differences in EC₅₀ values at under the three different salinity regimes. In general, lower salinity (20 psu) induced a significant decrease in percent spore release of U. pertusa as estimated by a decrease in EC₅₀ values, while higher salinity (40 psu) reduced the toxicity of metals as shown by an increase EC₅₀ values. These findings enable one to predict that any additional increase in pollution status would result in a pronounced reduction in the distribution of U. pertusa in brackish and estuarine waters.     

The toxicity of chromium,nickel and zinc: effects of salinity and temperature,and the osmoregulatory consequences in the mysid Praunus flexuosus

The effect of salinity (4.5–27ℵ) and temperature (5 and 15°C) on the acute toxicity of chromium, nickel and zinc to the mysid crustacean Praunus flexuosus (Müller) has been investigated, at time intervals up to 300 h. Increased metal concentration led to reduced median survival time. Increased temperature, and salinities above or below the isosmotic point, led to reduced median survival times at a given metal concentration and reduced median lethal concentrations of metals. The effect of salinity on metal toxicity has been clearly linked to disruption of the normal pattern of hyper/hypoosmoregulation. The death of animals in chromium or zinc solutions may be related to a progressive decrease in the ability of the animals to osmoregulate, with the rate of osmotic decline related to the median survival time, or the loss of osmoregulatory ability may be a secondary effect of metal poisoning and dying. Nickel was found to be less toxic than either chromium or zinc and to have less effect on osmoregulation.     

The effects of humic substances on copper toxicity to Ceriodaphnia silvestrii Daday (Crustacea, Cladocera)

A major question in the field of ecotoxicology is how DOM affects copper accumulation and toxicity in planktonic organisms; copper acute toxicity and bioaccumulation in Ceriodaphnia silvestrii were investigated in the presence and absence of humic substances (HS) under controlled laboratory conditions. Copper was determined as free Cu2+ ions in the media and total copper in the animals; metal ion buffers were used for ion selective electrode calibration, extending the lower detection limit to 10(-11) mol l(-1). Groups of 20 adult females of similar sizes were exposed (24 h) to a range of nominal copper concentrations. Based on total added copper, LC50 was 4.4 x 10(-8) mol l(-1) without HS, whereas with 20 mg l(-1) HS, it was 25 times higher (1.1 x 10(-6) mol l(-1)). Based on free Cu2+ ions LC50 was statistically similar either with (2.8 x 10(-8) mol l(-1)) or without HS (3.3 x 10(-8 )mol l(-1)). The present results showed that natural DOM reduced copper toxicity and that free Cu2+ ions correlates to the bioavailable fraction to zooplankton. Nevertheless, copper bioaccumulation by C. silvestrii was similar either in the presence or absence of humic substances, suggesting that C. silvestrii regulates its body copper content up to 3.0 x 10(-8) mol l(-1) free Cu2+ ions in the media. The organisms were not able to deal with higher free Cu2+ ions concentrations in the media.     

Effect of temperature on heavy metal toxicity to earthworm Lumbricus terrestris (Annelida: Oligochaeta)

Earthworms (Lumbricus terrestris) acclimated at 2 degrees C above their habitat temperature (10-12 degrees C) showed about 5% increase in basal rate of oxygen consumption, which increased to about 38% in 14-16 degrees C- and 40% in 16-18 degrees C-, but decreased by 84% in 20-22 degrees C-acclimated worms. Temperature also increased the blood hemoglobin (Hb) concentration, which decreased slightly in 20-22 degrees C-acclimated worms. The worms acclimated at 20-22 degrees C showed their blood to be hypovolemic than that of 10-12 degrees C worms indicating dehydration. Pre-exposure of 10-14 degrees C-acclimated worms to sublethal concentrations of zinc, copper, and lead did not significantly affect the rate of respiration. However, at higher temperatures all these metals inhibited oxygen consumption; zinc, lead, and cadmium by approximately 11% and copper by approximately 18% of that at 14-16 degrees C. At 20-22 degrees C, the respiration was further inhibited, 36% by copper, 18% by cadmium, and approximately 10% by lead and zinc. Copper, lead, and zinc decreased the temperature-enhanced increase in blood Hb concentration at all temperatures. In 20-22 degrees C-acclimated worms heavy metal exposure slightly lowered the oxygen affinity of Hb as well as caused shifts in carbon monoxide difference spectra. The acute toxicity of these metals was not affected by a 2 degrees C rise in acclimation temperature but increased by 17% (lead), 33% (copper), and 5% (zinc) in 14-16 degrees C- and by 40% (lead), 149% (copper), and 132% (zinc) in 20-22 degrees C-acclimated worms. The increase in toxicity of metals caused by high temperatures may be due to limiting the scope of aerobic metabolism (oxygen extraction, transport, and utilization) via quantitative and qualitative effects on Hb. This terrestrial species appears to be tolerant of slight increases in habitat temperature, such as that expected with current global climate change.     

Acute toxicity of organic chemical mixtures to the fathead minnow

The acute joint toxicity of industrial organic chemicals to the fathead minnow was determined for binary and equitoxic multiple chemical mixtures. Results from binary tests were used to define isobole diagrams. The degree of joint toxic action was determined among 27 chemicals from seven different chemical classes. The slopes of the acute concentration response relationships were quite similar for all test chemicals. This suggests that the mode of acute toxic action for these chemicals is alike though it may not be identical. Intoxication signs of fish exposed to nearly all test chemicals were also similar and indicative of an anesthetic like effect. The results of isobole diagrams for binary mixtures, with 1-octanol as the reference chemical, demonstrated a near concentration additive acute joint action over a wide range of mixture ratios for each chemical from 7 different classes. Tests conducted with mixtures containing equitoxic levels of two to 21 chemicals also displayed a concentration additive acute joint action. All test chemicals can be modeled by a structure-toxicity relationship characteristic of a narcosis type of toxic action. These results are consistent with those of other investigators and are of particular importance when one realizes that numerous industrial chemicals are likely to cause lethality to aquatic organisms through similar toxic action.     

Chelation in metal intoxication. XXIX: Alpha-mercapto-beta-aryl acrylic acids as antidotes to mercury (II) toxicity

alpha-Mercapto-beta-(2-furyl) acrylic acid (MFA), alpha-mercapto-beta-(phenyl) acrylic acid (MPA), alpha-mercapto-beta-(2-hydroxyphenyl) acrylic acid (MHA), alpha-mercapto-beta-(4-methoxyphenyl) acrylic acid (MMA), beta-1,2-phenylene di-alpha-mercapto acrylic acid (1, 2-PDMA) and beta-1, 4-phenylene di-alpha-mercapto acrylic acid (1, 4-PDMA) enhanced faecal excretion and reduced liver, spleen and blood burden of inorganic mercury when administered (0.5 m mol/kg, in two split doses) 24 hr after Hg (II) (1 mg/kg) in rats. MFA, MPA, MHA, and MMA were also effective in lowering renal Hg mainly from the cytosol, without any significant increase in urinary excretion of Hg. The results indicate that all the mono-mercapto acrylic acids including MFA were more effective than di-mercapto acrylic acids and act through the mechanism characteristic of thiol chelators, that is, mobilization of Hg as their complexes, contrary to the reported observation that MFA acts through the induction of metallothionein.     

Effect of temperature on heavy metal toxicity to juvenile crayfish, Orconectes immunis (Hagen)

The acute toxicity of four selected heavy metals to juvenile crayfish Orconectes immunis (Hagen) (1-2 g wet body wt. each) at room temperature increased in the following order: cadmium (x3) < copper (x10) < zinc (x2) < lead. The toxicity of these metals to crayfish acclimated at 17, 20, 23/24, and 27 degrees C increased with temperature (by 7-20% between 20 and 24 degrees C and 14-26% between 20 and 27 degrees C) as judged by the lowering of LT(50) (time to kill 50% of test animals at a fixed concentration) values. A 4 degrees C rise in temperature (from 20 to 24 degrees C), which increased the toxicity of copper by about 7%, increased the rate of oxygen consumption by about 34%. Heavy metals inhibited the rate of oxygen consumption at all temperatures. In 20 degrees C-acclimated crayfish, copper caused about 17% inhibition of oxygen consumption compared to about 7-12% by other metals including the most toxic cadmium. A 3-4 degrees C rise in temperature tripled the inhibitory effect of copper (20%), cadmium and zinc (26 and 18%, respectively), but not of lead, on oxygen consumption. A 7 degrees C-rise in temperature (from 20 to 27 degrees C) increased the inhibitory effect of heavy metals, including lead, on oxygen consumption by up to 54% in the case of copper. The data indicate that rising global temperatures (currently 0.60 degrees C) associated with climate change can have the potential to increase the sensitivity of aquatic animals to heavy metals in their environment.     

Physiological and behavioural responses of Gammarus pulex (Crustacea: Amphipoda) exposed to cadmium

The aim of this study was to investigate the effects of cadmium on physiological and behavioural responses in Gammarus pulex. In a first experiment, cadmium LC50s for different times were evaluated in 264 h experiment under continuous mode of exposure (LC50(96 h)=82.1 microgL(-1), LC50(120 h)=37.1 microgL(-1), LC50(168 h)=21.6 microgL(-1), LC50(264 h)=10.5 microgL(-1)). In a second experiment, the physiological and behavioural responses of the amphipod exposed to cadmium (0, 7.5 and 15 microgL(-1)) were investigated under laboratory conditions. The mortality and the whole body cadmium concentration of organisms exposed to cadmium were significantly higher than in controls. Concerning physiological responses, cadmium exposure exerted a significant decrease on osmolality and haemolymph Ca(2+) concentration, but not on haemolymph Na(+) and Cl(-) concentrations, whereas the Na(+)/K(+)-ATPase activity was significantly increased. Behavioural responses, such as feeding rate, locomotor and ventilatory activities, were significantly reduced in Cd exposed organisms. Mechanism of cadmium action and consequent energetic reallocation in favour of maintenance functions (i.e., osmoregulation) are discussed. The results of this study indicate that osmolality and locomotor activity in G. pulex could be effective ecophysiological/behavioural markers to monitor freshwater ecosystem and to assess the health of organisms.     

Nutritional status of Carcinus maenas (Crustacea: Decapoda) influences susceptibility to contaminant exposure

Using the shore crab Carcinus maenas as a model, this study tested the hypothesis that nutritional status influences susceptibility of adult crabs (>60mm carapace width (CW)) to environmental contamination. In the laboratory, crabs were either starved, given a restricted diet (fed on alternate days) or fully fed (fed each day). In addition, crabs under each feeding regime were exposed to a sublethal concentration (200microgl(-1)) of pyrene (PYR) as a model organic (PAH (polyaromatic hydrocarbon)) contaminant. Various physiological end points were measured after 7 and 14 days. Results indicated that adult shore crab physiology was relatively robust to short-term (7 days) nutritional changes as multivariate analysis (ANOSIM) showed no significant difference in shore crab physiological condition between control and pyrene-exposed crabs, irrespective of dietary feeding regime [Global R=0.018, P (%)=19.2]. After 14 days, however, starved crabs showed significant impacts to physiological condition (as revealed by multivariate analysis) [Global R=0.134, P (%)=0.1], [R=0.209, P (%)=0.1]; starved individuals had significantly lower antioxidant status (F(2,48)=5.35, P<0.01) compared to crabs under both types of feeding regime. Exposure to pyrene resulted in significantly elevated pyrene metabolite concentrations in the urine at 7 and 14 days compared with control individuals (P<0.001), validating contaminant bioavailability, and this was found for all dietary treatments. Also, exposed crabs had significantly increased protein levels (proteinuria) than controls (P<0.001) in their urine after 7 and 14 days, irrespective of dietary regime. After 7 days, pyrene-exposed crabs showed significantly increased antioxidant status (P<0.001) and cellular functioning (increased cellular viability and decreased phagocytosis) (P<0.001) compared to control crabs; however, after 14 days, antioxidant status (P<0.01) and cellular viability (P<0.001) were significantly decreased in pyrene-exposed compared to unexposed crabs. Results indicate that differences in nutritional status of adult crabs result in shore crabs being robust to short-term sublethal (7 days) pyrene exposure. Susceptibility to contaminant exposure, however, was measured after prolonged exposure (14 days) as indicated by reduced ability to combat oxidative stress. These results indicate that ecotoxicological studies need to take into account the nutritional state of the test organism to achieve the full assessment of contaminant impact. In addition, the results highlight that subtle seasonal biotic features of an organism can influence biomarker responses, and these need to be considered when interpreting field data and during the routine application of biological-effects tools in environmental monitoring.     

Modes of metal toxicity and impaired branchial ionoregulation in rainbow trout exposed to mixtures of Pb and Cd in soft water

Models such as the Biotic Ligand Model (BLM) predict how natural organic matter (NOM) and competing ions (e.g., Ca(2+), H(+) and Na(+)) affect metal bioavailability and toxicity in aquatic organisms. However, such models focus upon individual metals, not metal mixtures. This study determined whether Pb and Cd interact at the gill of rainbow trout (Oncorhynchus mykiss) when trout were exposed to environmentally relevant concentrations of these metals (Cd<100nmolL(-1); Pb<500nmolL(-1)) in soft (<100mumolCa(2+)L(-1)), moderately acidic (pH 6.0) water. The 96-h LC50 for Pb was 482nmolL(-1), indicating that Pb was one-order of magnitude more toxic in soft, acidic water than in harder, circumneutral pH waters. The LC50 for Cd alone was also low, 6.7nmolL(-1). Surprisingly, fish acclimated to soft water had multiple populations of Pb-gill and Cd-gill binding sites. A low capacity, high affinity population of Pb-gill binding sites had a B(max) of 18.2nmolg(-1) wet weight (ww) and apparent logK(Pb-gill)=7.05, but a second low affinity population could not be saturated up to free Pb concentrations approaching 4000nmolL(-1). Two populations of Cd-gill binding sites were characterized: a high affinity, low capacity population with an apparent logK(Cd-gill)=7.33 and B(max)=1.73nmolg(-1) ww, and a low affinity, high capacity population with an apparent logK(Cd-gill)=5.86, and B(max)=13.7nmolg(-1) ww. At low concentrations, Cd plus Pb accumulation was less than additive because Cd out-competed Pb for gill binding sites, which were likely apical Ca(2+)-channels. While disturbances to Ca(2+) influx were caused by Cd alone, Pb alone had no effect. However, Pb exacerbated Cd-induced disturbances to Ca(2+) influx demonstrating that, although Pb- plus Cd-gill binding was less than additive due to competition, the effects (ionic disturbances) were more than additive (synergistic). Pb was also likely binding to intracellular targets, such as branchial carbonic anhydrase, which led to inhibited Na(+) influx. This ionic disturbance was exacerbated by Cd. We conclude that exposure to environmentally relevant concentrations of Pb plus Cd results in less than additive metal-gill binding in soft, moderately acidic waters. However, ionic disturbances caused by Cd plus Pb are greater than additive, and this may ultimately increase the toxicity of Cd-Pb mixtures to fishes. Our findings suggest that it may be necessary to re-evaluate water quality criteria and assumptions of the BLM for fish exposed to mixtures of Pb and Cd in the acidic, soft waters found in the Canadian Shield, Scandinavia and other sensitive regions.     

Thermoresponsive hydrogels with low toxicity from mixtures of ethyl(hydroxyethyl) cellulose and arginine-based surfactants

Ethyl(hydroxyethyl) cellulose (EHEC) is known to form hydrogels in water at elevated temperatures in the presence of an ionic surfactant. In this paper, the potential use of arginine-based surfactants is explored considering the production of a low toxicity thermoresponsive hydrogel for pharmaceutical and biomedical applications. The interactions between EHEC and the monomeric surfactant N(α)-lauroyl-l-arginine methyl ester (LAM) and two gemini surfactants N(α),N(ω)-bis(N(α)-acylarginine) α,ω-dialkyl amides were evaluated by Rheo-Small Angle Light Scattering measurements. The complex viscosity of the systems was dependent on surfactant concentration and temperature. Under specific conditions, soft gels of homogeneous structure were produced. The cloud point (CP) of the EHEC-LAM system varied significantly with surfactant concentration, while only moderate CP changes were found in the presence of the gemini surfactants. Finally, the effect of the surfactants on the viability of a human cell line was evaluated. Despite the lower toxicity of LAM, the superior gel forming efficiency of the gemini surfactants at lower concentrations revealed their advantageous suitability as components of a biocompatible thermoresponsive gel system.     

Hydrophobicity-dependent QSARs to predict the toxicity of perfluorinated carboxylic acids and their mixtures

Perfluorinated carboxylic acids (PFCAs) have wide industrial applications because of their unique physicochemical characteristics. However, data on the toxicity of much of this chemical class is lacking, particularly with regard to mixture toxicity. In this study, the toxicity of individual PFCAs and their mixtures to Photobacterium phosphoreum were observed. There was a tendency of increasing toxicity from C3 to C14 PFCA and a tendency of decreasing toxicity from C14 to C18 PFCA because of “the maximum tolerance of the cell membrane”. Using the equivalent log K_OW (octanol–water partition coefficient) and log K_SD (C₁₈-Empore™ disks/water partition coefficient), two linear quantitative structure–activity relationship (QSAR) models were formulated. This indicated both K_SD and K_OW can describe the hydrophobicity of a single chemical. However, for the PFCA mixtures, K_MD is the more reasonable parameter than K_owmix to describe the hydrophobicity because only the equivalent log K_MD could be used to predict the mixture toxicity.     

The combined toxicity assessment of carp (Cyprinus carpio) acetylcholinesterase activity by binary mixtures of chlorpyrifos and four other insecticides

Mixtures of organophosphate (OP) and carbamate (CB) insecticides are commonly detected in freshwater habitats. These insecticides inhibit the activity of acetylcholinesterase (AChE) and have potential to interfere with behaviors that may be essential for survival of species. Although the effects of individual anticholinesterase insecticides on aquatic species have been studied for decades, the combined toxicity of mixtures is still poorly understood. In the present study, we assessed whether pesticides in a mixture act in isolation (resulting in additive AChE inhibition) or whether components interact to produce either antagonistic or synergistic toxicity. Brain AChE inhibition in carp (Cyprinus carpio L.) exposed to a series of concentrations of the OP (chlorpyrifos, malathion and triazophos) as well as the CB (fenobucarb and carbosulfan) were measured. The concentration addition (CA) model and the isobole method were used to determine whether toxicological responses to binary mixtures of pesticides. In 50:50 % effect mixtures, the observed combined toxicity of chlorpyrifos and malathion was significantly higher than observed and was considered as synergistic. For equivalent dose mixtures, when chlorpyrifos mixed with fenobucarb or malathion, the observed toxicities were significantly higher than predicted, suggesting synergistic joint actions. The rest five binary combinations exhibited concentration additive or slight antagonistic joint actions. The CA model and the isobole method provided estimates of mixture toxicity that did not markedly underestimate the measured toxicity, therefore these methods are suitable to use in ecological risk assessments of pesticide mixtures.