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In this study, the concentration of six metal(loid)s was examined in the fish Oreochromis aureus collected from El Comedero dam during a massive mortality event induced by a mine tailing spill. A major spill (~ 300,000 m3) of waste was released into the San Lorenzo River System following a rupture in the tailing dam of a mining plant in NW Mexico; consequently, the discharged material flowed into El Comedero dam. The accumulation of metal(oid)s in the tissues of O. aureus showed higher levels in the liver than in the guts and muscle. Concentrations in the liver were high (As, 1.1–1063; Cd, 8.9–392; Cu, 372–59,129; Hg, 0.46–19.79; Se, 8.7–748; and Zn, 116–820 μg g−1), revealing that these fish were exposed to high concentrations of these elements. The mortality of fish could have resulted from the combined effect of the six analyzed metal(loid)s, as well as other residues present in mine tailings. [ABSTRACT FROM AUTHOR]

During January 2013, a mining spill occurred in the Santa Maria mining region, releasing around 300,000 m 3 of tailings on Los Remedios river, which was transported through the San Lorenzo river and finally to El Comedero (EC) dam. Twenty months later, we examined the concentrations of Hg and Se in the muscle, liver, gills, and guts of three fish species (Cyprinus carpio, Oreochromis aureus, Micropterus salmoides) captured in the EC dam to assess the performance of the cleaning operations. A high Se concentration in the liver of all species (carp, 1.2 ± 0.4; tilapia, 3.9 ± 2.1; bass, 3.5 ± 1.1 µg g -1 ww) was consistently observed, while this behavior was only found in the blue tilapia for Hg (0.15 ± 0.11 µg g -1 ww). Tilapia (benthic-detritivorous) exhibited the highest Se concentrations compared to the carp (omnivore) and the largemouth bass (piscivore). In contrast, the largemouth bass had the highest Hg levels in the muscle compared with the other fishes. Such differences could be related to the different metabolism and feeding habits among species. Compared to a tilapia study carried out three months after the mine spill during a mortality event, a decrease was evident in the liver for Se and Hg by 7.2 and 4.7 times, respectively. This reveals that cleaning operations were more efficient for Se and less for Hg, and that a prolonged period was required for the partial recovery of the element levels in fish from sites impacted by mining. Considering the Mexican consumption scenarios for each fish species, it could be concluded that there will be no non-cancer risk by exposure to Hg or Se., (© 2023. The Author(s).)

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 LC 50 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 (HgCl 2 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., Competing Interests: Declaration of competing interest The authors Javier Ramírez-Rochín, Ángel I. Campa-Córdova, Martín G. Frías-Espericueta, Marcela G. Fregoso-López, Irasema E. Luis-Villaseñor and Federico Páez-Osuna of the manuscript titled “Acute mercury toxicity and bioconcentration capacity in shrimp Litopenaeus vannamei juveniles: effect of low salinity and chemical speciation” submitted to Science of the Total Environment declare the have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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 LC 50 , respectively. No significant differences were found among As LC 50 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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Two experimental modules with different stocking densities (M1 = 70 and M2 = 120 shrimp m -2 ) were examined weekly during 72-day culture cycle at low-salinity water (1.9 g L -1 ) and zero-water exchange to examine the effects of water quality deterioration on the antennal gland (AG) of shrimp. Results showed survival rates of 87.7% and 11.9% in M1 and M2, respectively. Water temperature, pH, dissolved oxygen, and chlorophyll a were not significantly different between modules but the concentrations of the nitrogen compounds were significantly different between modules with the exception of nitrite-N, showing a higher histological alteration index in M2 (32 ± 10) than M1 (22 ± 0) with a strong correlation with the nitrogen compounds. During the last weeks was evidenced in M1 inflammation and hemocytic and hemolymph infiltration, while in M2, melanization, hemocytic melanized nodules and cells with kariorrexis.