Mercury bioaccumulation in zooplankton and its relationship with eutrophication in the waters in the karst region of Guizhou Province, Southwest China

Mercury dynamics at the base of the pelagic food web of the Gulf of Gdańsk, southern Baltic Sea

Planktonic organisms, which have direct contact with water, serve as the entry point for mercury (Hg), into the marine food web, impacting its levels in higher organisms, including fish, mammals, and humans who consume seafood. This study provides insights into the distribution and behavior of Hg within the Baltic Sea, specifically the Gulf of Gdańsk, focusing on pelagic primary producers and consumers. Phytoplankton Hg levels were primarily influenced by its concentrations in water, while Hg concentrations in zooplankton resulted from dietary exposure through suspended particulate matter and phytoplankton consumption. Hg uptake by planktonic organisms, particularly phytoplankton, was highly efficient, with Hg concentrations four orders of magnitude higher than those in the surrounding water. However, unlike biomagnification of Hg between SPM and zooplankton, biomagnification between zooplankton and phytoplankton was not apparent, likely due to the low trophic position and small size of primary consumers, high Hg elimination rates, and limited absorption.

Concentration of mercury and other metals in an Arctic planktonic food web under a climate warming scenario

Arctic marine ecosystems act as a global sink of mercury (Hg) and other metals, and high concentrations of these have been measured in higher trophic-level organisms. Nevertheless, the concentrations of metals at the basis of the marine food web in the Arctic is less known despite the likelihood of biomagnification from dietary sources. We investigated the concentrations of mercury (Hg) and other metals in different size fractions of plankton in West Greenland. All size fractions contained detectable levels of Hg (ranging from 4.8 to 241.3 ng g dw-1) at all stations, although with high geographic variability, likely reflecting the sources of mercury (e.g., meltwater). In many cases, the concentrations in the larger-size fractions were lower than in the smaller-size fractions, suggesting depuration through the metabolic activity of mesozooplankton. Concentrations of Cd, Pb, V, Ni, and Cr were higher than previously reported elsewhere in the Arctic.

Mercury and methylmercury in Hg-contaminated paddy soil and their uptake in rice as regulated by DOM from different agricultural sources

In this study, from the perspectives of structural and compositional variations of soil-dissolved organic matter (DOM), we explored the effects of agricultural DOM inputs on methylmercury (MeHg) accumulation in the soil and mercury (Hg) bioaccumulation in rice grains. Pot experiments with the addition of DOMs from maize straw (MaS), rape straw (RaS), rice straw (RiS), composted rice straw (CRiS), cow dung (CD), and composted cow dung (CCD) were then conducted. Results showed that, relative to the control, the DOM amendment from each agricultural source elevated MeHg concentrations in the soil, with an increase of 18-227%, but only parts of DOMs elevated total dissolved Hg (DHg) and MeHg (DMeHg) concentrations in pore water. Among all DOM species, RiS, CRiS, and CCD significantly increased total Hg (THg) and MeHg contents in rice grains by 34-64% and 32-118%, respectively. Compared with RiS, THg and MeHg contents in rice grains in the CRiS treatment decreased slightly, which was consistent with the distributions of DHg and DMeHg concentrations in pore water and the aromaticity variation of soil DOM. In contrast, the CCD input significantly enhanced the enrichment of THg and MeHg in rice grains relative to CD because it significantly reduced the humification of soil DOM at all rice-growing stages while increasing the low-molecular-weight fractions in soil DOM. The THg and MeHg contents in the rice grains were significantly lower treated by RaS than those by MaS and RiS, which may be related to the higher sulfur-containing compounds such as sulfate and cysteine in rape straw or its DOM solution. Overall, DOM amendment from different agricultural sources resulted in significantly discriminative effects on the MeHg accumulation in soil and Hg enrichment in rice in the Hg-contaminated paddy field by shaping soil DOM properties.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Arsenic and Mercury Distribution in an Aquatic Food Chain: Importance of Femtoplankton and Picoplankton Filtration Fractions

Arsenic (As) and mercury (Hg) were examined in the Yellowstone Lake food chain, focusing on two lake locations separated by approximately 20 km and differing in lake floor hydrothermal vent activity. Sampling spanned from femtoplankton to the main fish species, Yellowstone cutthroat trout and the apex predator lake trout. Mercury bioaccumulated in muscle and liver of both trout species, biomagnifying with age, whereas As decreased in older fish, which indicates differential exposure routes for these metal(loid)s. Mercury and As concentrations were higher in all food chain filter fractions (0.1-, 0.8-, and 3.0-μm filters) at the vent-associated Inflated Plain site, illustrating the impact of localized hydrothermal inputs. Femtoplankton and picoplankton size biomass (0.1- and 0.8-μm filters) accounted for 30%-70% of total Hg or As at both locations. By contrast, only approximately 4% of As and <1% of Hg were found in the 0.1-μm filtrate, indicating that comparatively little As or Hg actually exists as an ionic form or intercalated with humic compounds, a frequent assumption in freshwaters and marine waters. Ribosomal RNA (18S) gene sequencing of DNA derived from the 0.1-, 0.8-, and 3.0-μm filters showed significant eukaryote biomass in these fractions, providing a novel view of the femtoplankton and picoplankton size biomass, which assists in explaining why these fractions may contain such significant Hg and As. These results infer that femtoplankton and picoplankton metal(loid) loads represent aquatic food chain entry points that need to be accounted for and that are important for better understanding Hg and As biochemistry in aquatic systems. Environ Toxicol Chem 2023;42:225-241. © 2022 SETAC.

Methylmercury bioaccumulation in water flea Daphnia carinata by AIEgen

Mercury ion (Hg²⁺) is a toxic heavy metal ion and Hg²⁺ is convertible to methylmercury (MeHg) by many aquatic microorganisms, leading to bioaccumulation and biomagnification in aquatic organisms, which can interfere with brain development and function in humans. This study employs a newly developed AIEgen (Aggregation-induced emission fluorogen) to quantify and visualise the process of MeHg bioaccumulation in vivo on the species of water flea Daphnia carinata. Two approaches to MeHg absorption were taken, either by direct incubation in a MeHg solution or by indirect consumption of algae contaminated with MeHg. We analysed the relationship between the ratio of photoluminescence (PL) intensities (I₅₈₅/I₄₈₀) and MeHg concentration (C_MeHg) and generated a master curve for determining MeHg concentration based on the measurement of PL intensities. Fluorescent image analysis showed the occurrence of MeHg in D. carinata to be mainly in the compound eyes, optic nerve and carapace. This study indicates that MeHg absorption can be quantified and visualised in the body of zooplankton, and the MeHg transfer to zooplankton is more likely through direct exposure than via indirect food intake. The accumulation of MeHg in the eye and the nervous system could be the cause of the high mortality of D. carinata exposed to MeHg in water.

Impact of Industrial Production, Dam Construction, and Agriculture on the Z-IBI in River Ecosystems: A Case Study of the Wanan River Basin in China

Industrial activity, dam construction, and agriculture—while important for socioeconomic progress—can severely damage the natural environment. To evaluate the effects of these human activities on the bio-integrity of riverine ecosystems, we examined the Wanan reach of the Ganjiang River (Wanan River basin), which contains the river’s largest reservoir. On the basis of 20 attributes of zooplankton, we constructed a zooplankton index of bio-integrity (Z-IBI) evaluation system using range analysis, discriminant analysis, and correlation analysis. Our research found that these anthropogenic activities can greatly change the composition and number of zooplankton community. The overall health status of this catchment was classified as “good”, and the eco-health situation of the reference, industrial, dam-controlled and agricultural sites were deemed “healthy”, “fair”, “good”, and “fair”, respectively. Our results suggested that the three activities adversely affected the integrity of local aquatic ecosystems. Agriculture was the activity most detrimental to the zooplankton community, followed by industrial production and dam construction. Therefore, we demonstrated that the Z-IBI evaluation system can be applied to reservoir–riverine ecosystems. We also provide guidance on the ecological protection, assessment, monitoring and of reservoir–riverine ecosystems and suggest that additional Z-IBI evaluation approaches be further developed in the future.

Persistent thallium contamination in river sediments, source apportionment and environmental implications

The adverse impacts of detrimental thallium (Tl) contamination are of increasing concerns to sustainable development. Herein, the contents, distributions and sources of Tl and potential toxic elements (PTEs) (Pb, As, Cr, Cu, Ni, Co, Sb, Cd and U) were investigated in sediments collected in Gaofeng River, which has been contaminated by long-term mining activities, located in Yunfu City, Southern China. Results indicated that excessive Tl levels were found in sediments (1.80-16.70 mg/kg). Sequential extraction procedure indicated that despite a large amount of Tl entrapped in residual fraction, a significant level of Tl (0.28-2.34 mg/kg) still exhibited in geochemically labile fractions, which was easy for Tl mobilization and availability. Pb isotope tracing method further confirmed that the pyrite exploitations may be the prime contaminated contributor (47-76%) to these sediments. These findings highlight that it is essential to establish more effective measures for Tl contamination control and call for engineered remediation countermeasures towards polluted river sediments.