Table 2 Papers assessing the impact of heavy metals on reproductive and infertility indices

Heavy metals

Moran-Martinez et al. (2013) [73]

Cross-sectional

Questionnaire-measurement

Exposed group N=20

Non-exposed group N=27 (Torreon Coahuila, Mexico)

Exposure to lead in the environment and workplace is associated with decreased sperm concentration and motility and increased abnormal sperm forms. there were significant differences in the spermatic concentration [EG=43.98±6.26 and NEG=68.78±8.51×10⁶ cell mL^-1 ((p<0.01), motility [EG=49±7 and NEG=67±4% (p=0.029)], viability [EG=36.32±3.59 and NEG=72.12±1.91% (p<0.01)], and abnormal morphology [EG=67±18 and NEG=32±12% (p<0.01)].

Xu et al. (2012) [74]

Cross-sectional

Questionnaire-measurement

96 males (China)

Arsenic entry into the body through a contaminated environment, water, and food may be associated with reduced semen quality and infertility.

(DMA concentrations above the median were significantly associated with below-reference sperm concentrations (P =0.02))

Wu et al. (2012) [75]

Prospective

Questionnaire-measurement

341 males (Taiwan)

High concentration of lead in semen was associated with reduced sperm count, but did not affect its volume, motility, and morphology. (the sperm count was negatively associated with semen lead concentration (r=0.130, P=0.0165).) Consequently, it can be concluded that heavy metals such as lead entry into the body through the environment and food have negative effects on human fertility by affecting the semen quality and count.

He et al. (2016) [76]

Experimental study

Measurement

20 males (China)

Environmental exposure to lead affects sperm function, which can subsequently reduce reproductive capacity in men, by reducing CAMP, calcium, and tyrosine phosphorylation.

Lei et al. (2015) [77]

Cross-sectional

Questionnaire-measurement

Infertile women (N=310)

Pregnant women (N=57) (Taiwan)

Serum levels of lead and arsenic were higher in infertile women than in pregnant women.

A significant difference was observed in the categorized frequencies of Chinese herbal medicine use between the groups (p < 0.01). In particular, an obvious difference was noted in infertile women taking Chinese herbal medicine 1–6 times per week compared with pregnant women (30.9 % versus 10.5 %). The blood Pb and As levels were also significantly higher in the infertile women than in the pregnant women (p < 0.01).

Mendiola et al. (2011) [78]

Case-control

Questionnaire-measurement

Exposed group (n = 30) Non-exposed group (n = 31) (Spain)

That association remained statistically significant after adjustment for age, BMI, and number of cigarettes per day (b= 1.5; 95% CI, 0.37, 1.9, and b= 4.9; 95% CI, 0.84, 9.1, respectively). An inter-quartile increase in seminal plasma concentrations of Pb (5.0 μg/L) and Cd (0.3 μg/ L) for a 33.5-year-old with a BMI of 23 kg/m² would be predicted to increase immotile sperms 21.6% and 24.3%, respectively.

Heavy metals (lead and cadmium) endanger reproductive health in men by affecting semen plasma levels and sperm motility.

Hsi et al. (2016) [79]

Cross-sectional

Questionnaire-measurement

N= 224 (Taiwan)

The concentration of methylmercury in the hair of infertile women (1.82 ± 0.14 mg/kg) was significantly higher than the of pregnant women (1.24 ± 0.18 mg/kg). As a result, exposure to mercury while consuming fish can reduce the fertility.

Meeker et al. (2008) [80]

Cross-sectional

Measurement

219 men) Michigan, USA(

There was a direct correlation between the serum level of molybdenum and a decrease in sperm concentration and normal morphology. As a result, it can be concluded that exposure to heavy metals (zinc, mercury, copper, cadmium, arsenic, etc.) endangers reproductive health in men by reducing the semen quality and damage to sperm DNA. [adjusted odds ratios (ORs) for below-reference semen quality parameters in the low, medium, and high Mo groups were 1.0 (reference) 1.4 [95% confidence interval (CI) 0.5–3.7], and 3.5 (95% CI, 1.1–11) for sperm concentration and 1.0 (reference), 0.8 (95% CI, 0.3–1.9), and 2.6 (95% CI, 1.0–7.0) for morphology]