This ecological study measured manganese in 158 drinking water samples from deep groundwater, shallow groundwater and surface water in 28 villages of Huai’an city. Concentrations were high and varied by season and source, and three quarters of samples exceeded the Chinese drinking water value of 100 µg/L. The authors report a positive village-level correlation with cancer incidence and mortality in the low-flow period only.
Key numbers
- All samples: mean 452.32 ± 507.76 µg/L (n = 158), minimum 0.02 µg/L, maximum 4364.00 µg/L; detection rate 100% (Results 3.2, p. 2; Table 1).
- By period: high-flow 265.47 ± 388.83 µg/L (n = 84); low-flow 664.41 ± 544.82 µg/L (n = 74) (Table 1, p. 2).
- By source (Table 1): surface water 506.33 ± 362.88 µg/L (n = 47); shallow groundwater 573.64 ± 672.47 µg/L (n = 55); deep groundwater 287.83 ± 370.25 µg/L (n = 56).
- Share of samples above 100 µg/L: 75.32% overall (119 of 158); 53.57% in the high-flow period and 100% in the low-flow period (Table 3, p. 3).
- Low-flow regression: each 1 µg/L increase in manganese associated with 0.45 per 100,000 more cancer cases (SE 0.13, p = 0.005) and 0.35 per 100,000 more cancer deaths (SE 0.11, p = 0.008) (Table 6, p. 4). High-flow correlations were not significant (Table 5).
Methods (brief)
About 500 mL of water per sample was acidified with nitric acid, stored at 4 degrees C and analyzed by ICP-MS. The Chinese national drinking water standard of 100 µg/L defined exceedance. Cancer incidence and mortality for 2008 to 2010 came from the city cancer registry and were related to village water concentrations by correlation and regression.
Evidence fitness
The water concentrations are usable occurrence data for rural drinking water sources in one Chinese region. The cancer associations are ecological and unadjusted for smoking, diet or other factors, as the authors acknowledge, so they cannot establish that manganese causes cancer.
Limitations
The text is internally inconsistent about the high-flow source means: one passage assigns 72.01 µg/L to deep groundwater, as Table 2 does, while another assigns it to surface water; Table 2 values are used here. Villages were selected for high cancer incidence. The paper’s conclusion that manganese “is carcinogenic to people” goes beyond its ecological design. No detection limit or reference material results are reported.
Related evidence
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