This Chinese field study compares water, soil, forage, grain, sheep tissues and human hair and blood from an area beside a zinc smelter in the Wumeng mountains with a control county. Zinc, copper, cadmium and lead were all higher in the affected area, and concentrations fell with distance from the smelter. The anemia and oxidative-stress findings are attributed by the authors to heavy metal contamination broadly, with cadmium and lead given the main role.
Key numbers
- Grain (dried at 80 °C, mg/kg): affected corn zinc 27.14 ± 2.53 vs control 17.14 ± 1.53; affected rice 33.53 ± 1.32 vs 13.57 ± 1.32; affected wheat 35.46 ± 2.43 vs 15.46 ± 1.41 (mean ± SE; P < 0.01 marked) (Table 2, p. 8).
- Soil zinc 218.16 ± 9.27 mg/kg in affected pasture vs 32.37 ± 1.91 control; forage 178.01 ± 6.36 vs 23.48 ± 2.67; irrigation water 12.57 ± 1.93 vs 0.015 ± 0.003 (table unit printed as mg/kg for all three) (Table 1, p. 8).
- Human hair zinc 99.63 ± 7.71 mg/kg in affected residents vs 67.63 ± 6.76 control; blood 14.82 ± 0.81 vs 6.81 ± 0.76 mg/kg (Table 6, p. 9).
- Sheep muscle zinc 141.13 ± 7.62 vs 113.56 ± 9.87 mg/kg; liver 233.93 ± 8.72 vs 137.79 ± 8.57; kidney 157.16 ± 7.43 vs 113.75 ± 7.69 (dried tissue) (Table 5, p. 9).
- Affected residents had hemoglobin 87.65 ± 6.56 g/L vs 131.78 ± 9.57 g/L in controls (Table 7, p. 10).
Methods (brief)
Environmental samples came from 48 sites 50 to 30,000 m from the smelter; grains were collected from a local resident’s farmland and dried before analysis. Zinc was measured by atomic absorption spectrophotometry after nitric acid and hydrogen peroxide digestion, with bovine liver SRM 1577a as a reference material. Groups were compared by Student’s t-test; results are mean ± standard error.
Evidence fitness
The study supports the point that zinc smelting raises zinc together with cadmium and lead in local soil, water, forage, grain and human hair and blood. It does not separate zinc effects from cadmium and lead effects, does not estimate human zinc intake, and its grain samples come from one farm area rather than a market survey.
Limitations
The affected human volunteers were selected because they showed anemia, so the comparison is not population based. The number of grain samples is not stated. The water table unit (mg/kg) is unusual for water. Blood was described as drawn from ten volunteers in one place and analyzed for 20 per group elsewhere.
Related evidence
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