Toxicity and accumulation of mercury in three species of crabs with different osmoregulatory capacities

Lead, mercury, and selenium alter physiological functions in wild caimans (Caiman crocodilus)

Environmental contaminants affect ecosystems worldwide and have deleterious effects on biota. Non-essential mercury (Hg) and lead (Pb) concentrations are well documented in some taxa and are described to cause multiple detrimental effects on human and wildlife. Additionally, essential selenium (Se) is known to be toxic at high concentrations but, at lower concentrations, Se can protect organisms against Hg toxicity. Crocodilians are known to bioaccumulate contaminants. However, the effects of these contaminants on physiological processes remain poorly studied. In the present study, we quantified Hg, Pb and Se concentrations in spectacled caimans (Caiman crocodilus) and investigated the effects of these contaminants on several physiological processes linked to osmoregulatory, hepatic, endocrine and renal functions measured through blood parameters in 23 individuals. Mercury was related to disruption of osmoregulation (sodium levels), hepatic function (alkaline phosphatase levels) and endocrine processes (corticosterone levels). Lead was related to disruption of hepatic functions (glucose and alanine aminotransferase levels). Selenium was not related to any parameters, but the Se:Hg molar ratio was positively related to the Na⁺ and corticosterone concentrations, suggesting a potential protective effect against Hg toxicity. Overall, our results suggest that Hg and Pb alter physiological mechanisms in wild caimans and highlight the need to thoroughly investigate the consequences of trace element contamination in crocodilians.

Acute mercury toxicity and bioconcentration in shrimp Litopenaeus vannamei juveniles: Effect of low salinity and chemical speciation

This study evaluated low salinity effect on acute Hg toxicity and bioconcentration capacity in L. vannamei juveniles (8.4 ± 0.7 g), because this species is frequently exposed to hypo-osmotic environments in its natural habitat, and in farming ponds. Hg LC₅₀ values were 1723, 1272, 983 and 536 μg L^-1 at salinity of 5 ppt (parts per thousand); 2203, 1740, 1340 and 873 μg L^-1 at 10 ppt; and 7013, 5693, 1759 and 1534 μg L^-1 at 25 ppt for 24, 48, 72 and 96 h, respectively. After 96 h, acute Hg toxicity in shrimp was significantly higher in salinity of 5 ppt than in 25 ppt; likewise, Hg bioconcentration in shrimp exposed to different Hg treatments was statistically greater in salinity of 5 ppt than in 25 ppt. The chemical speciation calculated in experimental waters suggested that neutral chemical Hg species (HgCl₂ and HgClOH) were the most bioavailable because their fractions (51-62%) increased when salinity decreased. Therefore, the inverse relationship between Hg toxicity and salinity was due to osmotic stress and the neutral chemical Hg species fractions that increased at lower salinities. Hg bioconcentration factors indicated that the higher Hg waterborne concentrations were the most saturated uptake and storage mechanisms in shrimp. Thus, Hg concentrations in organisms did not increase in proportion to waterborne Hg concentrations in the three salinities. These results support the hypothesis of an effect of low salinity on Hg toxicity and bioconcentration capacity in L. vannamei. The safe Hg concentrations 5.4, 8.7 and 15.3 μg L^-1 were proposed for shrimp exposed to salinity of 5, 10 and 25 ppt, respectively. This information allows recognizing risky environments for both wild and cultured healthy growth of these shrimp, which can help decision makers on coastal management and shrimp pond managers to have better water quality.

Effect of low salinity on acute arsenic toxicity and bioconcentration in shrimp Litopenaeus vannamei juveniles

This study investigated acute arsenic toxicity and bioconcentration capacity in Litopenaeus vannamei because it has been frequently exposed to lower salinities than its isosmotic point (25 g L^-1). Juveniles (9.9 ± 0.4 g) were exposed to low (5-10 g L^-1) and isosmotic salinity (25 g L^-1) levels; As values were 30.8, 20.2, 16.8 and 13.9 mg L^-1 at 5 g L^-1; 30.4, 19.1, 16.8 and 14.8 mg L^-1 at 10 g L^-1; 31.5, 19.0, 15.0 and 11.9 mg L^-1 at 25 g L^-1 at 24, 48, 72 and 96 h LC₅₀, respectively. No significant differences were found among As LC₅₀ values calculated for different salinity levels and same exposure times, concluding that low salinity did not affect shrimp sensitivity to As. Likewise, no significant differences were observed in As bioconcentration in shrimp exposed to the same waterborne As and distinct salinity, supporting the results of acute toxicity. Bioconcentration factors of As maintained a relatively stable tendency where all values (0.8 ± 0.2 to 1.7 ± 0.4) were statistically comparable to 1, indicating that As was accumulated in a similar proportion to waterborne As concentration at three salinity levels. This study proposed 135.3 ± 12.1 μg L^-1 for salinities from 5 to 25 g L^-1 as provisional safe As concentration. According to these results, the hypothesis that sustains an effect of low salinity on As acute toxicity and its bioconcentration capacity cannot be acceptable. Therefore, the information provided allows knowing the threshold levels of As in water to avoid ecological and economic losses.

Morphofunctional Alterations in Zebrafish (Danio rerio) Gills after Exposure to Mercury Chloride

Mercury (Hg) is a global pollutant that may exert its toxic effects on living organisms and is found in both aquatic and terrestrial ecosystems in three chemical forms; elemental, organic, and inorganic. The inorganic form (iHg) tends to predominantly accumulate in aquatic environments. The gill apparatus is a very dynamic organ that plays a fundamental role in gas exchange, osmoregulation, acid-base regulation, detoxification, and excretion, and the gills are the primary route of waterborne iHg entrance in fish. In the present work we investigated the morphofunctional and ultrastructural effects in Danio rerio gills after 96 h exposure to two low HgCl₂ concentrations (7.7 and 38.5 µg/L). Our results clearly demonstrated that a short-term exposure to low concentrations of mercury chloride resulted in gill morphology alterations and in the modifications of both Na+/K⁺-ATPase and metallothioneins (MTs) expression pattern. The main morphological effects recorded in this work were represented by hyperplasia and ectopia of chloride cells (CCs), lamellar fusion, increased mucous secretion, alteration of pavement cells (PVCs), detachment of the secondary epithelium, pillar cell degeneration, degeneration, and apoptosis. Trough immunohistochemistry and real-time PCR analysis also showed a dose-related modulation of Na⁺/K⁺-ATPase and MTs.

Mercury levels and health parameters in the threatened Olrog's Gull (Larus atlanticus) from Argentina

Mercury (Hg) exposure was investigated through feathers of Olrog's Gull and related to health parameters in adults (hematocrit, total plasma proteins, morphometric measures, sex) and chicks (hematocrit, total plasma proteins, immunoglobulins G and M) from a colony located in estuary of Bahía Blanca, Argentina. Mercury concentrations were 5.50 ± 2.59 μg g⁻¹ (n = 44) in live adults, 1.85 ± 0.45 μg g⁻¹ (n = 45) in live chicks and 1.81 ± 0.41 μg g⁻¹ (n = 41) in dead chicks. Large differences were observed between live adults and live or dead chicks and small differences between live and dead chicks. In the adults, the sex of the birds was the variable that best explained Hg concentrations. Male birds had higher concentrations than females; this suggests that the clutch provides a sink for mercury during egg laying. Hg concentrations in both adults and live chicks were associated with higher hematocrits. This could be associated with upregulated erythropoiesis to compensate for increased rate of destruction of prematurely senescent, Hg-contaminated erythrocytes. Based on our results, on the levels of Hg pollution in the past in the study area, and on the dietary specialization of Olrog's Gull, we must be vigilant about potential negative effects of Hg pollution on this population and recommend continued monitoring on this threatened species.

Effects of some metals on carbonic anhydrase from brains of rainbow trout

Carbonic anhydrase (CA) enzyme was purified from rainbow trout brain by Sepharose-4B-L: -tyrosine-sulfanilamide affinity chromatography. The enzyme was obtained with a specific activity of 2,275 EU mg(-1) and a yield of 22.5%. The sample obtained from the affinity column was used for kinetic properties and inhibition studies. Both optimum and stable pH were found as 9.0 in 1 M Tris-SO(4) at 4 degrees C, respectively. To check the purity and subunit molecular weight of enzyme, sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis was performed, and MW was found as approximately 29.0 kDa. The molecular weight of native enzyme was estimated to be approximately 27.3 kDa by gel filtration chromatography. The purified enzyme had apparent K (m),V (max), and k (cat) as follows: 0.92 mM, 0.207 micromol.min(-1) and 43.6 s(-1) for p-nitrophenylacetate. The inhibitory effects of Co(II), Cu(II), Zn(II), Ag(I), and Cd(II) on CA enzyme activity were determined using the esterase method under in vitro conditions at low concentrations of the corresponding metals. The obtained IC(50) values, which cause 50% inhibition on in vitro enzyme activity, were 0.05, 30, 0.31, 159, and 82.5 mM for cobalt, copper, zinc, silver, and cadmium, respectively. K ( i ) values were also calculated from Linewaever-Burk plots for these substances as 0.014, 27.68, 2.15, 193.86, and 94.18 for cobalt, copper, zinc, silver, and cadmium, respectively; it was determined that cobalt, silver and cadmium inhibited the enzyme competitively, copper inhibited noncompetitively while zinc inhibited the enzyme uncompetitively.

Enzymatic biomarkers in the crab Carcinus maenas from the Minho River estuary (NW Portugal) exposed to zinc and mercury

Zinc and mercury are common contaminants of estuaries and coastal ecosystems where they may induce adverse effects on the biota. Carcinus maenas is a key-species in several European estuaries, living in close association with the sediment where a considerable number of environmental contaminants, including zinc and mercury may accumulate. In the present study, the acute effects of zinc and mercury on C. maenas from the Minho River Estuary (NW Portugal) were investigated by using the activity of the enzymes cholinesterase (ChE), lactate dehydrogenase (LDH) and glutathione S-transferases (GST) as effects' criteria. Crabs were exposed for 96h to several concentrations of Zn(2+) (0, 1.84, 3.71, 7.39 and 14.79mg/l) or Hg(2+) (0, 0.09, 0.19, 0.37 and 0.74mg/l). The choice of Zn(2+) test concentrations was based on the LC50 value (14.86mg/l) determined in a first part of the study, while the choice of Hg(2+) concentrations was based on values from the literature. At the end of the bioassays, eye, muscle and hepatopancreas tissues were isolated and used for ChE, LDH and GST determinations, respectively. Zinc significantly inhibited ChE activity (p<0.05, EC50=14.68mg/l), caused significant alterations of GST activity (p<0.05) and induced LDH activity (p<0.05) at the exposure of 14.79mg/l. Mercury significantly inhibited ChE activity (p<0.001, LOEC=0.09mg/l, EC50=0.235mg/l) and increased both GST (p<0.05, LOEC=0.774mg/l) and LDH activities (p<0.05, LOEC=0.119mg/l). These results suggest that both metals interfere with cholinergic neurotransmission in C. maenas by inhibiting ChE activity. In addition, they also interfere with GST activity and this may reduce the capacity of detoxification of some chemicals and/or to increase the probability of oxidative stress to occur. Furthermore, both metals increase LDH activity, suggesting an interference with energy production pathways. Therefore, the presence of zinc and mercury in estuaries at concentrations in the mg/l or mug/l range, respectively, may have a negative impact on C. maenas.

Mercury burdens in Chinese mitten crabs (Eriocheir sinensis) in three tributaries of southern San Francisco Bay, California, USA

Chinese mitten crabs (Eriocheir sinensis), endemic to Asia, were first reported in the San Francisco Bay in 1992. They are now established in nearly all San Francisco Bay tributaries. These crabs accumulate more metals, such as mercury, than crustaceans living in the water column. Because their predators include fish, birds, mammals and humans, their mercury burdens have an exceptional potential to impact the ecosystem and public health. We sought to elucidate the potential threat of mitten crab mercury burdens in three adjacent streams in southern San Francisco Bay, one of which is known to be contaminated with mercury. Mitten crabs had hepatopancreas concentrations of total mercury and methylmercury that did not differ among streams. The maximum burden we measured was below the action level of 1 ppm recommended by the USEPA. Hepatopancreas concentrations of methylmercury declined with increasing crab size, suggesting a mechanism for mercury excretion and that predators might reduce mercury exposure if they select larger crabs. Because mercury may be heterogeneously distributed among tissues, estimation of the impacts of crab mercury burdens on the environment requires more data on the feeding preferences of predators.

Inhibitory effects of cadmium on carbonic anhydrase activity and ionic regulation of the estuarine crab Chasmagnathus granulata (Decapoda, Grapsidae)

This work was aimed at evaluating the gill carbonic anhydrase (CA) activity of the estuarine crab Chasmagnathus granulata exposed in vivo to cadmium, at different salinities. The in vivo effect of the specific inhibitor acetazolamide (AZ) was also assayed. Besides, the inhibition of CA activity by different heavy metals (cadmium, copper, zinc) and AZ were evaluated under in vitro conditions. For the in vivo assays, adult males were acclimated to salinities of 2.5 or 30/1000. The corresponding 96-h LC50 of cadmium was 2.69 mg l-1 at 2.5/1000, and > 50 mg l-1 at 30/1000. Cadmium only caused a significant lower CA activity than control at 2.5/1000. EC50 for CA inhibition was estimated to be 1.59 mg l-1 at 2.5/1000. Statistical differences in Na+ hemolymphatic levels (P < 0.05) were only detected at 2.5/1000, between 0 and 1.25 mg l-1 of cadmium, but no statistical differences were observed for Cl- levels at any assayed salinity. As CA inhibition registered at 2.5/1000 was followed by only changes in Na+ concentration, it is likely that cadmium exposure could differentially affect ions permeability, among others factors. The concentrations that inhibited in vitro 50% of enzymatic activity (IC50) were 2.15 x 10(-5), 1.62 x 10(-5), 3.75 x 10(-6) and 4.4 x 10(-10) M for cadmium, copper, zinc and AZ, respectively. The comparison with IC50 values of other aquatic species, indicates a higher CA sensitivity for C. granulata to pollutants.