Geographical association of heavy metal exposure and semen quality: A national multi-center study

Assessing the adverse effects of geographical heavy metal mixture exposure on human semen quality is challenging. Our study aims to quantify the impact of these heavy metals on semen quality under both individual and combined exposures.

We recruited 32,072 reproductive-age men from ten human sperm banks across 31 provinces in China during the period from 2019 to 2022. Geographical heavy metal exposure was quantitatively assessed using the inverse distance weighting algorithm. The Power of Determinant (PD) values were calculated using the Geodetector (GD) to assess the individual and interactive effects of six soil heavy metals on semen quality parameters, including semen volume, sperm concentration, sperm motility, and total sperm count. Exposure-response analyses were performed using a generalized linear mixed model (GLMM).

The final analysis included 30,916 reproductive-age men. The factor detector identified mercury (Hg) as the primary factor among six geographical heavy metals contributing to decreased semen count [PD values: sperm concentration = 0.095, total sperm count = 0.112]. This was followed by arsenic (As), cadmium (Cd), and copper (Cu). Interaction detector analysis revealed that mixed exposure to heavy metals enhanced their negative effects on semen quality, especially the combined exposure to Hg and As (with the highest PD values). GLMM models indicated a significant positive association between geographical Hg exposure and the risk of suboptimal total sperm count (P < 0.05). In the medium (T2) and high (T3) exposure groups, the odds ratios (95 % Confidence Interval [CI]) for sperm concentration were 1.43 (1.24, 1.64) and 1.22 (1.05, 1.42), respectively. Similar results were observed for As, Cd, and Cu.

Our study provides new evidence from the perspective of GD, indicating that geographic mercury exposure is the primary driving factor behind the decline in semen quality. Additionally, mixed exposure exacerbates the adverse effects of heavy metals on semen quality.