Min Jing, Ting Dai, Sisi Mo, Xiaolong Wang, Haiyu Yan
The rice-fish co-culture system (RFCS) is an important agricultural model in the karst region of Guizhou, China, where the high geological background of mercury (Hg) may lead to elevated Hg accumulation in rice and fish. However, rice-fish are also rich in beneficial n-3 polyunsaturated fatty acids (PUFAs), particularly EPA and DHA, which may offset some of the neurodevelopmental and cardiovascular risks associated with methylmercury (MeHg). Thus, assessing the risk-benefit trade-off between Hg accumulation and n-3 PUFA benefits in karst rice-fish is essential for evidence-based dietary guidance. This study collected rice-fish from three karst and three non-karst villages in Guizhou (n = 73). Total Hg (THg), MeHg, and n-3/n-6 PUFA concentrations were analyzed, and the Ginsberg model was applied to integrate MeHg risks with EPA+DHA benefits across multiple intake scenarios (24.8 - 300 g/day). Our results showed that THg and MeHg concentrations in karst rice-fish (39.6 ± 38.0 ng/g , range: 3.19 - 134.3 ng/g, and 16.3 ± 20.8 ng/g, range: 0.62 - 84.4 ng/g, respectively) were similar to those in non-karst samples and well below China's safety limit (0.5 mg/kg). Karst rice-fish exhibited higher EPA+DHA levels (30.9 ± 48.2 mg/100g, median 23.5 mg/100g) and a more favorable n-3/n-6 ratio (0.79 ± 0.78, median 0.64) than non-karst ones. The risk-benefit assessment indicated that karst rice-fish consumption provides a positive net effect on both adult cardiovascular health and infant neurodevelopment across all evaluated intake levels. Based on these findings, we recommend that local residents follow the Dietary Guidelines for Chinese Residents by consuming rice-fish up to 500 g/week. At this intake level, the health benefits of n-3 PUFAs consistently outweigh MeHg risks, with hair Hg concentrations remaining far below the safety threshold. We conclude that the positive effects of eating rice-fish from Guizhou's karst region clearly outweigh the potential Hg-related risks.