Increased Methylmercury Accumulation in Rice after Straw Amendment.

Area of Science:

• Environmental Science
• Agricultural Science
• Toxicology

Background:

• Rice is a dietary staple for many Asian populations.
• High rice consumption can lead to significant methylmercury (MeHg) exposure, especially with low fish intake.
• Understanding factors influencing MeHg in soil-rice systems is crucial for public health.

Purpose of the Study:

• To investigate the impact of straw amendment on methylmercury (MeHg) levels in Chinese paddy soils and rice grains.
• To elucidate the mechanisms behind increased MeHg accumulation in rice due to straw amendment.
• To assess the public health implications of this agricultural practice.

Main Methods:

• National-scale survey across 64 sites in China.
• Rice cultivation experiments.
• Batch incubation, seedling uptake, and sand culture experiments to study MeHg transformation and uptake.

Main Results:

• Straw amendment increased soil MeHg concentrations by 11-1043% and rice grain MeHg by 95%.
• Mechanisms include enhanced microbial methylation, increased MeHg mobility, greater rice root uptake, and improved translocation to grains.
• Fresh organic matter from straw enhances MeHg production and bioaccumulation.

Conclusions:

• Straw amendment, a widespread practice, significantly elevates methylmercury in rice.
• This practice increases neurotoxin exposure risks, necessitating policy review for straw management.
• Further research on mitigating MeHg accumulation in rice cultivation is warranted.