Microplastic contamination in wild shrimp Litopenaeus vannamei from the Huizache-Caimanero Coastal lagoon, SE Gulf of California

We identified and characterized microplastics (MPs) in the gastrointestinal tract (GT), gills (GI), and exoskeleton (EX) of Litopenaeus vannamei in a coastal lagoon from the SE Gulf of California. The most common MPs were fibers and fragments with an average size of 403 ± 296 μm, in which the transparent and blue colors predominated. The abundance (items/g as wet weight (ww)) in the GT, GI, and EX was 114.7 ± 33.2, 13.7 ± 5.3 and 3.0 ± 0.5, respectively. The abundance of MPs per shrimp was 13.3 ± 1.1, while the abundance per individual (ww) was 0.9 ± 0.2 MPs/g. Considering the consumption of shrimp in Mexico, MP abundance, and shrimp consumption (discarding GI and EX), we estimated MP ingestion as 280 items/person/year. The results from this study can be used as background information for future MP biomonitoring in shrimp species of ecological and commercial importance.

Synergistic effect of chloroquine and copper to the euryhaline rotifer Proales similis

Chloroquine (CQ) has been widely used for many years against malaria and various viral diseases. Its important use and high potential to being persistent make it of particular concern for ecotoxicological studies. Here, we evaluated the toxicity of CQ alone and in combination with copper (Cu) to the euryhaline rotifer Proales similis. All experiments were carried out using chronic toxicity reproductive five-day tests and an application factor (AF) of 0.05, 0.1, 0.3, and 0.5 by multiplying the 24-h LC₅₀ values of CQ (4250 µg/L) and Cu (68 µg/L), which were administered in solution. The rate of population increase (r, d^-1) ranged from 0.50 to 52 (controls); 0.20 to 0.40 (CQ); 0.09 to 0.43 (Cu); and -0.03 to 0.30 (CQ-Cu) and showed significant decrease as the concentration of both chemicals in the medium increased. Almost all tested mixtures induced synergistic effects, mainly as the AF increased. We found that the presence of Cu intensifies the vulnerability of organisms to CQ and vice versa. These results stress the potential hazard that these combined chemicals may have on the aquatic systems. This research suggests that P. similis is sensitive to CQ as other standardized zooplankton species and may serve as a potential test species in the risk assessment of emerging pollutants in marine environments.

The link between COVID-19 mortality and PM2.5 emissions in rural and medium-size municipalities considering population density, dust events, and wind speed

One contemporary issue is how environmental pollution and climate can affect the dissemination and severity of COVID-19 in humans. We documented the first case of association between particulate matter ≤2.5 μm (PM_2.5) and COVID-19 mortality rates that involved rural and medium-sized municipalities in northwestern Mexico, where direct air quality monitoring is absent. Alternatively, anthropogenic PM_2.5 emissions were used to estimate the PM_2.5 exposure in each municipality using two scenarios: 1) considering the fraction derived from combustion of vehicle fuel; and 2) the one derived from modeled anthropogenic sources. This study provides insights to better understand and face future pandemics by examining the relation between PM_2.5 pollution and COVID-19 mortality considering the population density and the wind speed. The main findings are: (i) municipalities with high PM_2.5 emissions and high population density have a higher COVID-19 mortality rate; (ii) the exceptionally high COVID-19 mortality rates of the rural municipalities could be associated to dust events, which are common in these regions where soils without vegetation are dominant; and (iii) the influence of wind speed on COVID-19 mortality rate was evidenced only in municipalities with <100 inhabitants per km². These results confirm the suggestion that high levels of air pollutants associated with high population density and an elevated frequency of dust events may promote an extended prevalence and severity of viral particles in the polluted air of urban, suburban, and rural communities. This supports an additional means of dissemination of the coronavirus SARS-CoV-2, in addition to the direct human-to-human transmission.

Single and mixture toxicity of As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, and Zn to the rotifer Proales similis under different salinities

Aquatic organisms that inhabit coastal environments are generally exposed to multiple mixtures of chemicals. The single and mixture toxicity of nine trace metals (As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, and Zn) to the rotifer Proales similis were examined at four different salinities (5, 15, 25, and 35 ppt). Chronic toxicity reproductive tests were performed using an application factor (AF) of 0.05, 0.1, 0.2, and 0.4 by multiplying the 24-h LC₅₀ values of each metal. The metal mixture treatments were: T1, As-Cd-Cr-Cu-Fe-Hg-Ni-Pb-Zn; T2, As-Cd-Hg-Pb and; T3, Cr-Cu-Fe-Ni-Zn. The LC₅₀ values ranged between 5 and 4140 μg L^-1 in the following order: Hg > Cu > Fe > Pb > Cd > Zn > As > Cr > Ni in low salinity and Hg > Cu > Fe > Pb > Zn > As > Cd > Cr > Ni in high salinity conditions. In all cases, acute toxicity was higher at a salinity of 5 ppt compared to 35 ppt. Chronic toxicity tests indicated that single metal toxicity intensified as the AF increased and as salinity decreased. Regardless of salinity, Pb at 0.4 AF was the most toxic metal. Proales similis evidenced a higher growth in the As treatments (0.1 and 0.2 AF) at 35 ppt compared to controls. Furthemore, the T1 and T2 treatments were the most toxic, and in most cases, they induced a synergistic effect. Antagonism effects were detected in the T3 treatment at 25 and 35 ppt. The present data highlights the importance of the examination of pollution in natural environmental conditions in which many aquatic invertebrates endure.

Effect of salinity and temperature on the acute and chronic toxicity of arsenic to the marine rotifers Proales similis and Brachionus ibericus

Several abiotic factors influence the ecological responses of aquatic invertebrates to metal toxicity. We examined the effect of salinity (10, 20, and 30 psu) and temperature (25 and 32 °C) on acute and chronic arsenic (As) toxicity to the euryhaline rotifers, Proales similis and Brachionus ibericus. In general, higher salinities and low temperature resulted in lower arsenic toxicity. The population growth studies indicated that P. similis was more sensitive than B. ibericus to As. Arsenic toxicity intensified the vulnerability of P. similis to B. ibericus competition. Life table parameters decreased with increasing As levels in the medium. Chronic toxicity bioassays were more sensitive than acute toxicity tests for determining the adverse effect of As to rotifers. Our findings provide useful insights on the effect of arsenic on rotifer populations exposed to different temperature and salinity scenarios. Proales similis could be an important complement to brachionid rotifers for marine toxicity bioassays.

Combined effects of temperature and salinity on the demographic response of Proales similis (Beauchamp, 1907) and Brachionus plicatilis (Müller, 1786) (Rotifera) to mercury

The demographic response of the brackish-water rotifers Proales similis and Brachionus plicatilis to mercury (0.5, 2, 8 and 32 μg L^-1 of HgCl₂) at different salinity levels (10 and 20‰) and two temperature (25 °C and 32 °C) regimes were evaluated. Median lethal concentration (LC₅₀) for P. similis and B. plicatilis was 10 and 16 μg L^-1, respectively, showing that Proales similis was more sensitive to mercury than B. plicatilis. The rate of population increase (r) for both species was greater at 10‰ salinity and 32 °C (ranged from 0.6 to 0.95 d^-1). The r-value decreased as the concentration of mercury in the medium increased. Regardless of the temperature, at lower salinity and higher mercury concentration (32 μg L^-1), P. similis died within six days. The survivorship of P. similis and B. plicatilis was higher at 25 °C than at 32 °C (ranged from 5 to 8 and 7-13 d, respectively). Fecundity was higher at 32 °C than at 25 °C for both rotifers species. There was a significant effect of the interaction among salinity, temperature, and mercury in both species on the reproductive variables such as net and gross reproductive rates, generation time and the rate of population increase. Considering the sensitivity of P. similis, we suggest that this species be included in the list of marine bioassay organisms.