Fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) is counted as an organic manganese (Mn)-derived compound. The toxic effects of Mn (alone and complexed) on dopaminergic (DA) neurotransmission have been investigated in both cellular and animal models. However, the impact of environmentally relevant Mn exposure on DA neurodevelopment is rather poorly understood. In the present study, the MMT dose of 100 μM (about 5 mg Mn/L) caused up-regulation of DA-related genes in association with cell body swelling and increase in the number of DA neurons of the ventral diencephalon subpopulation DC2. Furthermore, our analysis identified significant brain Mn bioaccumulation and enhancement of total dopamine levels in association with locomotor hyperactivity. Although DA levels were restored at adulthood, we observed a deficit in the acquisition and consolidation of memory. Collectively, these findings suggest that developmental exposure to low-level MMT-derived Mn is responsible for the selective alteration of diencephalic DA neurons and with long-lasting effects on fish explorative behaviour in adulthood.

Phosphorus (P) cycling present in sediments associated with iron (Fe), manganese (Mn) and sulfur (S) geochemical processes may cause secondary pollution in overlying water. Understanding the mechanisms of P release from sediments should help to restore water quality. This study used the diffusive gradients in thin film (DGT) technique to investigate the seasonal variation in the lability, remobilization mechanisms, and release characteristics of sediment P in the uncontaminated Xizhi River and the severely contaminated Danshui River, South China. P accumulation in sediments contributed to higher DGT-labile P concentrations in contaminated reaches, and the highest labile P concentrations were generally observed in summer season at each site. The significant positive relationships (p < 0.05) between labile Fe and P confirmed the Fe–P coupling release mechanism in uncontaminated sediments. Stronger relationships between labile Mn and P at contaminated sites indicated that Mn oxides played an important role in P remobilization. However, sulfate reduction associated with microbial activities (crucial genera: Desulfobulbus, Desulfomicrobium and Desulforhabdus) was considered to decouple the Fe & Mn–P cycling relationship, promoting P release at contaminated sites. The effluxes of sediment P were much higher in the Danshui River (mean 0.132 mg cm⁻²·d⁻¹) than in the Xizhi River (mean 0.038 mg cm⁻²·d⁻¹). And hot season led to growth in P effluxes that was much greater in contaminated river.

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was difficult to degrade in sediments. In this study, the environmental behavior of BDE-47 with/without the effect of benthos (Tubificidae Limnodrilus) and electron acceptors in sediments was investigated using C-14 tracer. Generally, extractable residues of BDE-47 were dominant in sediment and posed high environment risk. The amount of non-extractable residues (NERs) accounted for 39.0% of initial radioactivity in oxic sediments was significantly higher than those in anoxic sediments (17.6%). Most of NERs were localized in the humin fraction and presented as sequestrated forms. Under oxic conditions, the present of Limnodrilus significantly increased the proportion of NERs in sediment. Limnodrilus accumulated 34.2% of initial radioactivity. Under anoxic conditions, the addition of iron (Ⅲ) [Fe(III)], sulfate and nitrate reduced the environmental risk of BDE-47 with the increase of NERs formation, while manganese (IV) [Mn(IV)] addition had no effect on the formation of NERs. The present of Limnodrilus and electron acceptors promoted the production of metabolites. Meanwhile, BDE-47 changed the microbial community structure of sediments. These findings indicated that the environmental behavior and risk of BDE-47 was affected by benthos and electron acceptors, and the high proportion of sequestrated NERs posed high bioactivity and toxic threat to ecological environment.

Antarctic melt streams are important ecosystems that increasingly face contaminant pressures from anthropogenic sources. Metal contaminants are often reported in the limno-terrestrial environment but their speciation is not well characterised, making environmental risk assessments difficult. This paper characterises labile metal concentrations in five melt streams and three shallow lakes around the Casey and Wilkes research stations in East Antarctica using chemical extracts and field deployments of diffusive gradients in thin-film (DGT) samplers. An acute toxicity test with field-collected Ceratadon purpeus and taxonomic identification of diatoms in melt streams were used to infer environmental risk. Copper and zinc were the most labile metals in the melt streams. DGT-labile copper concentrations were up to 3 μg Cu L⁻¹ in melt-stream waters but not labile below the sediment-water interface. DGT-labile zinc concentrations were consistent above and below the sediment-water interface at concentrations up to 14 μg Zn L⁻¹ in four streams, but one stream showed evidence of zinc mineralisation in the sediment with a flux to overlying and pore waters attributed to the reductive dissolution of iron and manganese oxides. Other metals, such as chromium, nickel, and lead were acid-extractable from the sediments, but not labile in pore waters or overlying waters. All streams had unique compositions of freshwater diatoms, but one had particularly reduced diversity and richness, which correlated to metal contamination and sediment physico-chemical properties such as a finer particle size. In laboratory bioassays with field-collected samples of the Antarctic moss C. purpeus, there was no change in photosynthetic efficiency following 28-d exposure to 700, 900, 1060, or 530 μg L⁻¹ of cadmium, copper, nickel, and zinc, respectively. This study shows that microorganisms such as diatoms may be at greater risk from contaminants than mosses, and highlights the importance of geochemical factors controlling metal lability.

Most legacy mines contributed to contamination of the environment before and after cessation of mining. Contamination from waste rock, slag and tailings can introduce large concentrations of metals and metalloids to the surface soil and downstream sediments. Since ants are able to accumulate metals in their bodies, we investigated the possibility of using the elemental compositions of ants as indicators of metals at legacy mines developed on ores rich in copper (Cu), zinc (Zn), arsenic (As), silver (Ag) and lead (Pb). Our results showed the concentrations of manganese (Mn) and Cu in ants were not significantly different between mine and reference samples and only Zn was significantly different between contaminated and reference areas. Crematogaster spp. and Notoncus spp. from reference areas accumulated larger concentrations of metals in their bodies compared to ants from the mine. Ants accumulated metals in different parts of their bodies. The abdomen was the main site for accumulation of Mn, iron (Fe) and Zn. Mandibles were only associated with accumulation of Zn. Copper and Pb showed no area of preferential accumulation and traces were detected in the whole body of the ants. Ants from five genera had similar regions for metal accumulation. The exoskeleton did not contribute to accumulation of metals; instead all metals were stored in internal organs. Not all genera were suitable for use as indicators; only Iridomyrmex spp. and Ochetellus spp. accumulated larger amount of metals in mine samples compared to reference samples.

Studies of the association between prenatal exposure to metal elements and risk for neural tube defects (NTDs) have produced inconsistent results. Little research has examined the joint effects and interactions of multiple elements. This study examined 273 women with NTD-affected pregnancies and 477 controls. Cadmium, cobalt, chromium, copper, iron, mercury, manganese, molybdenum, lead, and zinc were quantified in maternal serum. Single and mixed effects of these elements on NTD risk were evaluated with Bayesian kernel machine regression, and the effects of individual elements were validated using logistic regression. As a result, NTD risk increased with the concentration of the mixture of the 10 elements. NTD risk rose as the levels of the five toxic elements increased, with effect sizes larger than the overall analyses, but they decreased, albeit non-significantly, as the levels of the five essential elements increased. Lead and manganese showed risk effects on NTDs, with odds ratios (ORs) of 1.94 (1.76–2.13) and 1.25 (1.14–1.38), respectively, with the remaining nine elements remaining at their median. Molybdenum showed a protective effect against NTDs with an OR 0.87 (0.90–0.94). The single-element results were validated using logistic regression. In conclusion, NTD risk increased with concentrations of the five toxic elements, with lead and manganese being the major contributors. Essential elements showed protective effects against NTD risk.

The present research used zebrafish (5–28 days post-fertilization; dpf) as a model organism to investigate the effects of chronic exposure to environmentally relevant sub-lethal concentrations of waterborne (261 μg/L) and dietary zinc (Zn) (1500 mg Zn/kg dw), either independently or simultaneously, during development. The results showed that whole body contents of Zn were increased in all Zn treatment groups, with the highest accumulation of Zn observed in larvae simultaneously exposed to elevated waterborne and dietary Zn. In addition, exposure to elevated levels of Zn, either through the water or the diet, led to a decrease in whole body calcium (Ca) contents at 28 dpf. The findings also suggested that exposure to elevated levels of Zn resulted in a significant reduction in whole body manganese (Mn) contents. More importantly, the magnitude of decrease in Mn contents by Zn exposure was markedly higher than that in Ca and appeared to mirror the increases in whole body Zn accumulation. These results indicate that Mn regulation is more sensitive than Ca to disruption by Zn exposure in developing fish. Further examination of the Zrt-Irt-Like Protein (ZIP) family of transporters using droplet digital PCR technologies revealed that several zip transporters exhibited temporal and exposure route-specific changes following Zn exposure. In particular, the level of zip4 was influenced by Zn exposure regardless of the exposure routes, while changes in zip7 and zip8 levels were predominantly driven by waterborne exposure. Overall, our findings demonstrated that zebrafish during the developmental periods are sensitive to elevated levels of Zn seen in the environment, particularly following co-exposures to waterborne and dietary Zn. Future toxicological assessment of elevated Zn exposure should consider both the exposure routes and the life stages of fish.

The relationship between heavy metal(loid)s exposure and oxidative stress damage is a matter of research interest. Our study aimed to investigate the distribution patterns of the nine heavy metal(loid)s in blood of pregnant women, including four toxic heavy metal(loid)s [arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg)] and five typical heavy metal(loid)s [manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn), and selenium (Se)] in blood. Blood samples of 348 women were collected and their concentrations in the serum (sr) and blood cells (bc) were measured, as well as serum heme oxygenase-1 (HO-1) (an oxidative stress marker). Total blood (tb) concentrations of these metal(loid)s and serum-to-blood cell concentration ratios (sr/bc) were further calculated. We found Cu mainly accumulated in the serum compared to the blood cells with Cuˢʳ/ᵇᶜ = 2.30, whereas Co, Se, and As evenly distributed between these two fractions. Other metal(loid)s mainly concentrated in the blood cells. Coˢʳ, Cuˢʳ, Cuᵇᶜ, Mnᵇᶜ, Znᵇᶜ, Cdᵇᶜ, Coᵗᵇ, Cuᵗᵇ, Mnᵗᵇ, Znᵗᵇ, Cdᵗᵇ, and Cuˢʳ/ᵇᶜ were negatively associated with serum HO-1, whereas Asˢʳ, Asᵇᶜ, Asᵗᵇ, Znˢʳ/ᵇᶜ, Cdˢʳ/ᵇᶜ, and Hgˢʳ/ᵇᶜ were positively, indicating of their potential toxicity. We concluded that the distribution patterns of blood heavy metal(loid)s, in particular for Cd, Hg and Zn, which either increased in serum or decreased in blood cells, might be associated with elevated serum oxidative stress, should be considered in environmental health assessments.

Pathogenic survivals were dramatically affected by Fe³⁺ and Mn²⁺ under freeze-thaw (FT), and the dissolutions of manganese and iron oxides (MIOs) were also accelerated under FT. But the mutual influences of pathogenic bacterial survival and MIOs under FT have not been profoundly explored yet. In this work, aqueous systems containing Escherichia coli as well as synthetic ferrihydrite (Fh) and manganese dioxide (MnO₂) were experimented under simulated FT cycles to study the mutual influences of metal oxides and bacteria survival while oxide dissolutions and appearances, bacterial morphology and activities (survival number, cell surface hydrophobicity (CSH) and superoxide dismutase (SOD)) were obtained. The results showed that broken E. coli cells by ice growth were observed, but both oxides promoted E. coli survival under FT stress and prolonged bacterial survival time by 1.2–2.9 times, which were mainly attributed to the release of Fe³⁺ and Mn²⁺ caused by FT. The dissolutions of Fh and MnO₂ under FT, which took place at a low level in absence of E. coli cells, were markedly enhanced with bacterial interferences by 2–8 times and higher dissolved manganese concentrations were detected than iron. This was probably because that concentrated organic matters which were released from broken cells, rejected into unfrozen liquid layer and acted as electron donors and ligands to oxide dissolution. Compared with Fh system, more significant promotion of E. coli survival under FT in MnO₂ systems were found because of more SOD generations associated with high dissolved manganese concentrations and the stronger cellular protection by MnO₂ aggregations. The results suggested that FT significantly influenced the interactions between metal oxides and bacterial in water, resulting to changes in pathogen activity and metal element cycling.

Lake sediments are widely used as environmental archives to reconstruct past changes in contaminants deposition, provided that they remain immobile after deposition. Arsenic (As) is a redox-sensitive element that may be redistributed in the sediments during early diagenesis, for instance along with iron and manganese, and thus depth profiles of As might not provide a reliable, unaltered record of past deposition. Here, we use inverse diagenetic modelling to calculate fluxes of As across the sediment-water interface and interpret As sedimentary records in eight lakes along a 80 km transect from the Giant and Con mines, Northwest Territories, Canada. The sediment cores were dated using ²¹⁰Pb methods and analyzed for solid-phase and porewater As, Fe, Mn and organic C concentrations. We reconstructed the history of As deposition by correcting for the varying mobility patterns and calculated contemporary As deposition fluxes. Correction for diagenesis was substantial for three of the eight lakes, suggesting that lakes with lower sedimentation rates, which allows longer residence of As within the reactive zones defined by the model, enhance the influence of diagenesis. Results show that solid phase As peaks coincides with the period of high emissions from past gold ore roasting activities. Results also show that sediments sustained present-day As fluxes to the water column of study lakes within 50 km of the mines, while sediment in study lakes further than 50 km acted as As sinks instead.