Manganese dioxide nanoparticles provoke inflammatory damage in BV2 microglial cells via increasing reactive oxygen species to activate the p38 MAPK pathway.

With the widespread use of manganese dioxide nanoparticles (nano MnO2), health hazards have also emerged. The inflammatory damage of brain tissues could result from nano MnO2, in which the underlying mechanism is still unclear. During this study, we aimed to investigate the role of ROS-mediated p38 MAPK pathway in nano MnO2-induced inflammatory response in BV2 microglial cells. The inflammatory injury model was established by treating BV2 cells with 2.5, 5.0, and 10.0 µg/mL nano MnO2 suspensions for 12 h. Then, the reactive oxygen species (ROS) scavenger (20 nM N-acetylcysteine, NAC) and the p38 MAPK pathway inhibitor (10 µM SB203580) were used to clarify the role of ROS and the p38 MAPK pathway in nano MnO2-induced inflammatory lesions in BV2 cells. The results indicated that nano MnO2 enhanced the expression of pro-inflammatory cytokines IL-1ß and TNF-α, elevated intracellular ROS levels and activated the p38 MAPK pathway in BV2 cells. Controlling intracellular ROS levels with NAC inhibited p38 MAPK pathway activation and attenuated the inflammatory response induced by nano MnO2. Furthermore, inhibition of the p38 MAPK pathway with SB203580 led to a decrease in the production of inflammatory factors (IL-1ß and TNF-α) in BV2 cells. In summary, nano MnO2 can induce inflammatory damage by increasing intracellular ROS levels and further activating the p38 MAPK pathway in BV2 microglial cells.

Increased Methylmercury Accumulation in Rice after Straw Amendment.

Consumption of rice has been shown to be an important route of dietary exposure to methylmercury (MeHg, a neurotoxin) for Asians having a low fish but high rice diet. Therefore, factors that increase MeHg production and bioaccumulation in soil-rice systems, could enhance the risk of MeHg exposure. On the basis of a national-scale survey in China (64 sites in 12 provinces) and rice cultivation experiments, we report that straw amendment, a globally prevalent farming practice, could increase MeHg concentrations in paddy soils (11-1043%) and rice grains (95%). By carrying out a series of batch incubation, seedling uptake and sand culture experiments, we demonstrate that these increases could be attributed to (1) enhanced abundances/activities of microbial methylators and the transformation of refractory HgS to organic matter-complexed Hg, facilitating microbial Hg methylation in soils; (2) enhanced MeHg mobility, and increased root lengths (35-41%) and tip numbers (60-105%), increasing MeHg uptake by rice roots; and (3) enhanced MeHg translocation to rice grains from other tissues. Results of this study emphasize fresh organic matter-enhanced MeHg production and bioaccumulation, and highlight the increased risk of MeHg after straw amendment and thus the need for new policies concerning straw management.

Incorporation of Decomposed Crop Straw Affects Potential Phytoavailability of Mercury in a Mining-Contaminated Farming Soil.

Recently, incorporation of crop straw into soils is being largely encouraged worldwide. To explore the possible influence of incorporation of decomposed crop straw on the speciation (i.e., inorganic mercury/IHg, and methylmercury/MMHg) and phytoavailability of mercury, mercury-contaminated farming soil was amended with different amounts (i.e., low, medium or high) of straw organic fertilizer (SF, mainly consisting of decomposed rice straw) or humus (HU) and incubated for a month. Potential phytoavailability of IHg, assessed by CaCl2 extraction, was significantly lower in soils amended with low/medium SF, possibly due to the immobilization effect of SF-organic matter on IHg. In contrast, phytoavailability of IHg was significantly higher in soils incorporated with high HU, possibly explained by the leaching effect of dissolved HU on soil-bound IHg. For MMHg, incorporation of medium/high HU significantly increased MMHg phytoavailability, while SF addition had little effect. Interestingly, MMHg levels in SF/HU amended soils were generally lower than that in soil receiving no amendment, probably because complexation of IHg with SF/HU organics decreased IHg availability to methylation microorganisms. Overall, current results suggested that incorporation of decomposed crop straw may have multiple effects on mercury biogeochemistry in soils, which should be considered when applying SF into mercury-contaminated farming soils.

Incorporating rice residues into paddy soils affects methylmercury accumulation in rice.

Paddy fields are characterized by frequent organic input (e.g., fertilization and rice residue amendment), which may affect mercury biogeochemistry and bioaccumulation. To explore potential effects of rice residue amendment on methylmercury (MMHg) accumulation in rice, a mercury-contaminated paddy soil was amended with rice root (RR), rice straw (RS) or composted rice straw (CS), and planted with rice. Incorporating RS or CS increased grain MMHg concentration by 14% or 11%. The observed increases could be attributed to the elevated porewater MMHg levels and thus enhanced MMHg uptake by plants, as well as increased MMHg translocation to grain within plants. Our results indicated for the first time that rice residue amendment could significantly affect MMHg accumulation in rice grain, which should be considered in risk assessment of MMHg in contaminated areas.

Combined and Relative Effect Levels of Perceived Risk, Knowledge, Optimism, Pessimism, and Social Trust on Anxiety among Inhabitants Concerning Living on Heavy Metal Contaminated Soil.

This research aims at combined and relative effect levels on anxiety of: (1) perceived risk, knowledge, optimism, pessimism, and social trust; and (2) four sub-variables of social trust among inhabitants concerning living on heavy metal contaminated soil. On the basis of survey data from 499 Chinese respondents, results suggest that perceived risk, pessimism, optimism, and social trust have individual, significant, and direct effects on anxiety, while knowledge does not. Knowledge has significant, combined, and interactive effects on anxiety together with social trust and pessimism, respectively, but does not with perceived risk and optimism. Social trust, perceived risk, pessimism, knowledge, and optimism have significantly combined effects on anxiety; the five variables as a whole have stronger predictive values than each one individually. Anxiety is influenced firstly by social trust and secondly by perceived risk, pessimism, knowledge, and optimism. Each of four sub-variables of social trust has an individual, significant, and negative effect on anxiety. When introducing four sub-variables into one model, trust in social organizations and in the government have significantly combined effects on anxiety, while trust in experts and in friends and relatives do not; anxiety is influenced firstly by trust in social organization, and secondly by trust in the government.

Effects of rice residue incorporation on the speciation, potential bioavailability and risk of mercury in a contaminated paddy soil.

To reduce air pollution, straw return instead of burning is being strongly encouraged in China, including some mercury polluted areas. Nevertheless, the possible influences of straw return on methylation, bioavailability and exposure risk of mercury were relatively unknown. In this study, different amounts of rice straw or root were added into a mercury contaminated soil. Potential bioavailability of soil-bound mercury to crops/deposit-feeders was assessed by quantifying extraction rates of mercury (%) by calcium chloride (CaCl2)/bovine serum albumin (BSA). Extraction rates of inorganic mercury (IHg) or methylmercury (MMHg) decreased significantly in rice residue amended soils, possibly due to the strong binding of mercury with organic matter in root/straw. Meanwhile, MMHg concentrations increased by 2-8 times in amended soils. Such increases were attributed to enhanced microbial activities and/or formation of Hg-S-DOM complexes after rice residue incorporation and decomposition. Consequently, potential exposure risk of IHg (quantified as concentration of potentially bioavailable mercury in soil) decreased significantly while that of MMHg increased up to 4 times. To our knowledge, this is the first study demonstrating that rice residue incorporation could significantly affect biogeochemistry of both IHg and MMHg in soils, which should be considered in straw incorporation activities in mercury polluted areas.