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Table 1 Effect of Environmental Factors on Semen Quality and Male Fertility: A Comparison of Human and Animal Studies

From: Impact of environmental factors on human semen quality and male fertility: a narrative review

S. no Predisposing factor Source/cause Human studies Animal studies
1 Air Pollution Motor vehicles exhaust, factories, fire, household, agriculture, waste treatment, oil refineries, natural sources, such as volcanic eruptions, wind, etc. PM2.5 in the air is directly associated with total sperm number and concentration [25, 128]
PM10 is related to semen volume and typical forms and inversely related to atypical forms [25, 129]
SO2 exposure at the time of sperm development causes oxidative damage to sperm [5]
Air pollution negatively affects testosterone levels [129]
PM2.5 exposure in mice causes a significant fall in sperm concentration, motility, serum testosterone levels, an increased percentage of morphological abnormalities in sperms [130]
•PM2.5 causes severe testicular damage on histopathology [131]
2 Chemicals
i. Dioxins/Furans Produced as a by-product of industrial and natural processes, such as smelting, chlorine bleaching of paper and pulp, production of pesticides, biomedical and plastic waste incineration Reduced sperm concentration and motility [47]
Ejaculate of infertile men had 2.2–2.3 times higher content of dioxins and furans as compared to their fertile counterparts [49]
Reduced daily sperm production, epididymis sperm counts, and dose-dependent histological changes in the testes [132]
Fall in plasma concentrations of testosterone, and LH [132]
ii. Bisphenol A
(BPA)
A major component of plastic and released during production, use, or disposal of plastics and break-down of industrial plastic-related wastes Pro-oxidative/apoptotic mitochondrial dysfunction [56]
Inverse correlation between sperm concentration and urinary BPA levels [67]
Reduced sperm production, motility, increased sperm abnormalities, acrosomal and sperm plasma membrane damage, decreased mitochondrial activity and, increased defective spermatozoa [58, 133]
Reduced serum concentrations of testosterone, LH [58]
iii. Pesticides/
Herbicides
Used in agriculture, to control insects Reduced sperm motility, sperm count, concentration, and increased sperm morphological abnormalities [134, 135] Reduced sperm motility, motion kinematic parameters, sperm ATP levels, and increased morphological modifications [136, 137]
iv. Phthalates Found in numerous consumer products, such as toys, pharmaceuticals, cosmetic products, building and construction materials, scent retainers, some medications, and personal care products Reduced total sperm counts, sperm concentration, larger sperm head sizes, an increased number of morphologically abnormal sperm lead to reduced semen quality [86, 87] Reduced sperm motility, capacitation, and acrosome reaction, leading to poor fertilization in mice [138]
Increased DNA fragmentation and decreased sperm motility in dogs [139]
v. Heavy Metals Volcanic eruptions, Weathering of metal-bearing rocks, mining, and industrial and agricultural activities Increased blood Cadmium and Barium levels and higher seminal lead, Cadmium, Barium, and Uranium result in low sperm viability and increased immotile sperm [94, 96]
Uranium levels correlate with decreased sperm motility and abnormal sperm morphology [94]
Exposure to high CuSO4 (250 µg/ml) and CdCl2 (500 µg/ml) results in reduced sperm motility [97]
Acute and chronic cadmium exposure causes reduced sperm motility, viability, and acrosome reaction both in vivo and in vitro [140]
Heavy metals adversely affect testicular morphology, sperm production, and quality [141]
3 Heat Exposure Occupational exposure in people working in furnaces, bakeries, welding, ceramic factories, laundries, dry cleaning shops, or drivers, hot climate, excessive use of hot tubs, Jacuzzi, or hot baths Extremes of temperature result in decreased semen quality including reduced sperm concentration, total sperm count, total motility, progressive motility [120]
Reduced sperm concentration and total amount per ejaculate in summers as compared to winters [121]
Heat stress causes a rise in sperm abnormalities, lipid peroxidation, altered mitochondrial function, decreased sperm motility, plasma membrane integrity, increased DNA fragmentation, and reduced sperm quality [118, 142, 143]
Heatwave conditions (5–7 °C above the optimum temperature for 5 days) adversely affect male reproductive potential, halve male fertility, and severely affect sperm competitive ability [144]