Impact of Environmental Pollution on Female Reproduction
Abstract
The increased pollution in the world atmosphere is a global concern. Water, air, and soil are polluted by various sources, such as farm fertilizer, sewage industrial waste products, fumes, and plastics, which in turn impact human health. Plastics and other mixtures of waste affect live in the water. Moreover, the ecosystem is disrupted by the use of heavy metal-containing chemicals in agriculture, and those are eventually consumed by humans. The consequences are a significant negative impact on health including reproductive health, which impairs fertility in the human population. Reproductive functions are severely affected by different chemicals which may interfere with hormonal functions. Greater consequences are faced by the women as the number of germ cells present in the ovary is fixed during fetal life, and which are nonrenewable. From the production of ovum to fertilization, to implantation, and finally continuation of pregnancy, all are affected by the heavy metals and endocrine disruptors. Lifestyle modifications such as consumption of organic foods, plastic product avoidance, separation of residential areas from industrial/agricultural areas, proper waste disposal, and so on, may help to improve the situation.
INTRODUCTION
Female reproduction includes the production of ovum, fertilization, protection, and nourishment of the fetus until birth. Starting from her maternal womb to her whole reproductive life, it is a long journey. There are lots of barriers during this journey which may interfere in every step from the production of ovum, to fertilization, to the passage and implantation of embryos, and finally continuation of the development of embryos to complete the term of the pregnancy. Environmental pollution is one of the important barriers to human reproduction that negatively affects both male and female fertility in several ways. Pollution in the environment exerts harmful effects on the ecosystem, including soil, water, air, and foods due to the presence of harmful chemical, biological, and physical substances (Murali Krishna and Manickam, 2017; Rai, 2016). Global industrialization contributes significantly to the environmental pollution, affecting countries across the globe. The necessary measures to prevent such pollution is equally difficult and expensive. People are exposed to many toxicants from poor environments and their health is at risk of many diseases including reproductive failure.
Reproductive failure encompasses infertility and miscarriages. Infertility can be defined as failure to conceive after 12 months of unprotected coitus. There are many causes of infertility among females. Ovulatory dysfunction is one of the important causes among others. Environmental pollutants and stressors have an adverse effect on ovulatory function causing follicular atresia, failed fertilization, implantation failure, and miscarriages (Carré et al., 2017; Conforti et al., 2018; Forgacs et al., 1997; Tian and Diaz, 2012; Xue and Zhang, 2018).
In this review, we want to explore the effect and mechanism of different heavy metals (HMs) (which contaminate foods), air pollutants, microparticles, and endocrine disruptors (EDs) on female reproduction.
ASSOCIATION OF ENVIRONMENT AND REPRODUCTION
Environmental contamination can result from different chemicals as they degrade and remain in the air, soil, drinking water, food, consumer product, and household dust. In a study in the United States, it is shown that detectable levels of different chemicals including phthalates and pesticides were detected in 99% to 100% of pregnant women (Woodruff et al., 2011). Gametes and early prenatal embryos are highly sensitive to stressors. Prenatal exposure to environmental toxicants causes many adult diseases particularly type 2 diabetes and coronary artery disease (Guidice et al., 2017). It is believed that intrauterine environment has a causal relationship with the origin of chronic adult disease (Barker, 1990, 1992; Barker et al., 1989). Although environmental pollutants can seriously damage male reproduction, the negative impact can be attenuated by the presence of spermatogonial stem cells in the seminiferous tubules, which are sufficient for maintaining fertility throughout the male lifespan (Skakkebaek, 2003). In contrast, female fertility potential is fixed as a fixed number of oocytes undergo atresia and apoptosis from intrauterine life till menopause without any replenishment due to the absence of stem cells (Wagner et al., 2020). This phenomenon is natural and the follicular pool declines according to the increment of the age of the women. But any insult which aggravates follicular atresia reduces the chance of fertility and reproductive life of a woman. Moreover, the production of the fertilizable oocyte is a long and complex process dependent on the strict collaborative function of the germinal and somatic compartment of the follicle and the coordinated action of different hormones in the body. Some of the environmental pollutants are EDs, which mimic endogenous hormones and interfere with the finest orchestration of the ovulatory process leading to anovulation and follicular destruction.
Environmental factors can be classified as
1. | Heavy metals | ||||
2. | Air pollutants | ||||
3. | Endocrine disruptors | ||||
4. | Climate change |
Heavy metals (HM)
HMs accumulate in the soil, water, and food chain and enter into the human body by drinking water and ingestion of foods. They stay in the body for a long time as they are very resistant to decomposition in natural conditions. Not all HMs are harmful to the body. Moreover, some are essential for body function in trace amounts. Copper, chromium, manganese, and zinc are essential trace elements for bodily function and are needed at very low concentrations but became toxic at higher concentrations. On the other hand, cadmium (Cd), mercury (Hg), and lead (Pb) have no metabolic function and are toxic at all doses. Contaminated drinking water is the main source, which contains a mixture of the abovementioned metals, arsenic, nickel (Ni), and chromium (Cr). River and sea contamination accumulates HMs in many fish like swordfish, tuna, and sharks. People who consume these fish frequently are at higher risk of HMs intoxication and different health hazards.
Another potential source of HM is active and/or passive exposure to cigarette smoking. Occupational exposure to different industrial processes which use these metals, rechargeable Ni-Cd batteries, jewelry, color pigments, toys, and bullet (Chan and Egeland, 2004) are other sources of HM contamination.
It is well known that environmental toxicants are responsible for inducing cardiovascular, renal, and neuronal damage and increased the risk of cancer and diabetes. Due to the increased incidence of infertility in recent years, researchers are trying to explore the possible detrimental effects of HMs on human fertility. HMs affect fertility in both sexes in many ways and the effect is more pronounced in females as they have a fixed and nonrenewable pool of germ cells in the ovary, which get exhausted within a short period of time. The adverse effect happens at different stages of reproductive life of a woman from fetal life to puberty and maturity (Bloom et al., 2010; Nandi et al., 2011) Chronic exposure to some HMs like Cd and Ni cause steroidogenic dysfunction, fetal abnormalities, and embryotoxicity as they act as EDs and interfere the production and activity of endogenous hormones and their receptors (Aquino et al., 2012). Moreover, oxidative stress due to the presence of HMs releases reactive oxygen species (ROS) affecting the physiological function of hormones and gamete and embryo quality leading to infertility (Rzymski et al., 2015). During pregnancy exposure to HMs leads to oxidative stress of the placenta and liberation of ROS, which causes preterm birth (Singh et al., 2018). The placental barrier cannot block the passage of all toxic substances and nonessential metals can cross the barriers due to their size, posing a potential risk to the fetus. Investigators showed the association between HMs concentration in the placenta and abnormal growth and development of the fetus, even severe fetal damage (Falcon et al., 2003; Llanos et al., 2009).
Effects of individual HMs
Mercury (Hg)
Mercury is released into the atmosphere via coal combustion, waste incineration, mining, and other industrial processes. It leaches into the water and accumulates in highly hazardous forms methylmercury (MeHg) and ethylmercury (EtHg) in freshwater fish, in food chain, and in ecosystem. Tuna, swordfish, mackerel, and sharks are highly contaminated with mercury. The safe concentration of mercury is 8μg/L, however, blood concentrations as high as 200μg/L might be detected among high consumers of such fish. Other sources of mercury exposure are broken thermometers, dental supplies, and fluorescent lamp manufacturing factories (Calafat et al., 2008; Woodruff et al., 2011).
Mercury is one of the HMs which affects both male and female fertility. Though there are many studies exploring the effect of mercury on male fertility, studies on female fertility are relatively less. Mercury alters the function of oestrogen and penetrates the placenta inducing spontaneous abortions, premature births, and congenital defects (Choe et al., 2003).
Lead (Pb)
Lead dust is usually liberated from the friction of opening and closing of windows or doors with lead-based paint, from contaminated soil, from chipping or flaking exterior lead-based paint, from the disposal of lead-containing products like batteries, from drinking water where the pipe contains lead, from food which is stored in ceramic dishes or pottery, and from cosmetics like kohl. Experiments on monkeys showed that continuous exposure to Pb over time, or exposure of adolescent monkeys to Pb with 35μg/dL in the blood causes decreased production of gonadotropin and oestrogen resulting in menstrual irregularities, spontaneous abortion, and fetal anomalies (Foster, 1992). Other experiments demonstrated that the mice which were exposed to lead in its intrauterine life experienced a preimplantation loss of embryo in its adult life with a reduced number of placental cell proliferation in the implanted embryo (Garg et al., 2015; Wide, 1985; Wide and D’Argy, 1986; Wide and Wide, 1980).
In humans, there are controversies regarding the effect of lead on pregnancy. Though a few studies did not find any relationship between lead intoxication and spontaneous abortion (Faikoğlu et al., 2006; Valentino et al., 1984), many studies showed a significantly high rate of spontaneous abortion and stillbirth in women who experienced lead intoxication during their childhood (Davis and Svendsgaard, 1987; Hertz-Picciotto, 2000; Hu, 1991). As lead can be transferred during pregnancy and lactation, a significant amount of lead can be accumulated in humans during childhood. A pregnant woman’s lead intoxication interferes with the development of the ovary of her female child, which might critically affect fertility in the child’s adult life (Weinberg et al., 1989).
Cadmium (Cd)
After years of exposure, Cadmium can be accumulated in the body. Cadmium levels can be measured in blood, urine, nail, hair, and saliva. Cadmium can be found in rechargeable batteries and food rich in fiber, that is, vegetables, cereals, potatoes, and spinach. A major source of Cd is the inhalation of dust, fumes, and cigarette (both active and passive) smoking. Cd interferes with the biosynthesis of progesterone by decreasing the expression of enzymes essential for steroidogeneses like P450 and 3β-hydroxysteroid dehydrogenase (3β-HSD) (Kawai et al., 2002). It also activates the oestrogen receptor by binding to the hormone-binding domain of the receptor (Stoica et al., 2000) resulting in delayed puberty/menarche, menstrual disturbances, hormonal deficiencies, loss of pregnancy, premature births, and low birth weights (Debby, 2018). There is a relation between iron deficiency (due to menstrual blood loss) and increased gastrointestinal absorption of Cd, which explains the high concentration of Cd in women of reproductive age in comparison to menopausal women and men (Akesson et al., 2002; Berglund et al., 1994). Its damaging effect persists as the half-life is 10–30 years. Therefore, maintenance of the appropriate level of iron is important to reduce the absorption of Cd (Vahter et al., 2004).
Zinc (Zn), Cobalt (Co), Nickel (Ni)
Both high and low levels of Zn have a negative effect on reproduction. Zn deficiency can negatively affect oocyte maturation, cumulus expansion, and ovulation. Meiotic arrest and cumulus expansion are two important Zn-dependent ovarian processes (Tian and Diaz, 2012). Zn deficiency can cause adverse effects during pregnancy like premature birth, low birth weight, and congenital defect. It also increases the susceptibility to diseases during adult life (Beaver et al., 2017; Castillo-Durán and Weisstaub, 2003; Maret and Sandstead, 2006). A high level of zinc can also cause (normal 70–120μg/dl) (Mashhadi et al., 2017) defective embryogenesis to even teratogenicity and lethal effects (Hurley and Swenerton, 1966).
Co is an essential part of vitamin B12, which is needed at a very low concentration for the formation of red blood cells but is toxic at high concentrations (Simonsen et al., 2012). Its daily intake ranges from 1.7 to 100μg/day. Increased concentration of Co in humans causes menstrual problems, lactation problems, and altered menopause (Sengupta et al., 2014).
In an animal study, it is shown that NiSO4 inhibited ovulation, abolished progesterone production, disturbed menstrual cycles, decreased implantation of the embryo, and increased embryo resorption (Forgacs et al., 1997). In humans, evidence is very sparse, even though embryotoxicity and carcinogenicity have been documented (Forgacs et al., 2012).
Air pollution
For the life of humans, air inhalation is a must for oxygen. Air keeps humans alive, but it shortens the length of life if it is polluted. According to data of IQ Air, 13%–22% of deaths are due to air pollution. According to the data from the Air Quality Life Index (AQLI), the average person is set to lose 2.2 years of their lives due to poor air quality. Residents of the most polluted areas of the world could see their lives cut short by 5 years or more (Energy Policy Institute at the University of Chicago [EPIC], September 2021). In Bangladesh, life expectancy is reduced to 6.5 years in the most polluted areas.
Every day people are breathing and ingesting different particles and chemicals which also enter the food chain through contamination of soil and water. The pollutants are particulate matters (PM 10, 2.5–10, and 2.5μm), which include ozone (O3), benzopyrene (BAP), polychlorinated biphenyls (PCBs), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), organic compounds, and HMs. Such pollutants are released abundantly from transport vehicles and industries. Women who are exposed to these toxicants during pre- and periconceptional periods produce abnormal oocytes and embryos leading to infertility and abortion. Air pollutants are responsible for abnormal gametogenesis and poor reproductive performance (Carré et al., 2017; Conforti et al., 2018). Toxicants induce abnormal endocrine function, oxidative stress, and inflammation are the main mechanisms by which they affect the ovary (De Coster and Van Larebeke, 2012; Iorio et al., 2014; Palmerini et al., 2017; Paro et al., 2012). Different studies have shown that women living in highly industrialized areas have a significant reduction of the antral follicle count, reduced number of fertilizable oocytes, and higher implantation failure, in comparison to women who live in the less polluted areas (Conforti et al., 2018; De Coster and Van Larebeke, 2012). PM 2.5 is found to impair sperm and oocyte quality and decrease fertility rate by 2% per 10μg/m3 increment of fine particles (Xue and Zhang, 2018). HMs and PMs have oestrogenic, anti-oestrogenic, and androgenic activities. These are responsible for impaired gonadal steroidogenesis and gametogenesis. Air pollution accelerates reproductive aging by decreasing ovarian reserve (Carré et al., 2017; Conforti et al., 2018; Gaskins et al., 2019). Santi et al. (2019) reported that there is a link between higher air pollution and lower levels of AMH. They observed a significant reduction of AMH in women living in the worst-polluted areas which indicates that environmental factors can interfere with ovarian physiology. In animals, exposure to PM 2.5 before conception showed the developmental arrest of inner cell mass trophectoderm differentiation of blastocyst, defective post-implantation embryonic development and a higher rate of abortions (Maluf et al., 2009). Even in a short period of exposure to a high concentration of PM10 is associated with a high rate of first trimester pregnancy loss (Perin et al., 2010). It is also evident that for people who are residing within 200m of the busy highways and heavy traffic areas, the fertility rate drops significantly (Nieuwenhuijsen et al., 2014). SO2, CO, NO2, PMs, and O3 significantly increase the risk of miscarriage and stillbirth (Yang et al., 2018). Air pollution-induced oxidative stress and inflammation leads to abnormal placentation and fetal development (Leiser et al., 2019). Lee and colleagues have shown that first-trimester exposure to particulate matter <2.5μm and ozone increased the risk of obstetrical complications like preeclampsia, gestational hypertension, preterm delivery, and small for date babies (Lee et al., 2013). Moreover, perinatal exposure to air pollution has also been associated with lower intelligence quotient (IQ) at 5 years of age (Edwards et al., 2010) and lower cognitive function at 8–11 years of age (Suglia et al., 2008). Decreased placental gene expression due to the influence of fine particulate matter cause neurodevelopmental problems in babies (Saenen et al., 2015).
The smoke of cigarette contains benzene that stimulates follicular depletion, increases basal follicle-stimulating hormone (FSH), and accelerates menopause by 3–4 years (Alviggi et al., 2014; Mattison et al., 1989). Presence of benzene at a level of >0.54ng/mL is associated with high FSH, significant reduction of E2, and the least number of oocyte retrieval in IVF (Xue and Zhang, 2018).
Another important component of air pollution is pesticides. Pesticides enter the body by the dermal and inhalation routes. The most common group of people affected by pesticides are farmers who have the highest chance of exposure to sprayed pesticides (Damalas and Koutroubas, 2016). People who live in areas treated with pesticides are also subjected to being polluted by direct spray diffused from neighboring fields. Mancozeb is a fungicide that is widely used to protect the most commonly used vegetables and fruits like potato, tomato, grape, apple, and banana. Given mancozeb is used by spraying, people may easily get affected by inhaling the polluted air. Even with its lower toxicity, mancozeb impairs fertilization and embryonic development in female mice when exposed to high doses (500mg/mL) (Rossi et al., 2006). Even in smaller doses (0.001–1μg/mL), mancozeb alters granulosa cell morphology and mitochondrial metabolism of the oocyte (Iorio et al., 2014; Palmerini et al., 2018; Paro et al., 2012). Not only mancozeb but also the sprayed pesticides interfere fertilization of oocytes leading to infertility (Cecconi et al., 2011).
Endocrine disruptors (EDs)
EDs are chemicals that can interfere with the function of endocrine systems. We are exposed to them through the environment, food, and skin. They interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the development, behavior, fertility, and maintenance of normal bodily functions. EDs mimic or block the function of endogenous hormones. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders.
Common EDs are Bisphenol-A (BPA), Phthalates, Dioxin, Atrazine, Perchlorate, Fire Retardants, Lead, Arsenic, Mercury, PCBs, Perfluorinated chemicals (PFCs), Organophosphate pesticides and glycerol ether. ED can be categorized into persistent and non-persistent types. PCB, DDT is persistent ED which are lipophilic chemicals stored in the body for a prolonged period (>10 years) (Rodprasert et al., 2011). These bio-accumulative substances are present almost everywhere in the environment (Gregoraszczuk and Ptak, 2013). Man-made, exogenous substances such as BPA, parabens, triclosan, phthalates, synthetic pyrethroids, and organophosphate pesticides are non-persistent types (Dziewirska et al., 2018).
Polychlorinated biphenyls
PCB had been extensively used and found in electrical, coolant, and hydraulic devices until it was banned in 1979 under Toxic Substance Control Act in the United States. Although it is banned, it still can be found in the products, which were made before this time (US Environmental Protection Agency). PCB is very stable once released into the environment and bio cumulative. It is found to be stored in aboveground food crops, plants, fish, and animals. Moreover, they can be transported a long distance from its sources. Ingestion of contaminated food and occupational environment are common sources of human exposure. As this compound can persist in the environment and in the human body for decades, it is still considered a health concern. These chlorinated hydrocarbons are capable of disrupting follicular steroidogenesis by altering the hormonal properties, synthesis, and function. Moreover, it is found in follicular fluid, ovarian tissue, uterine layers, placenta, and amniotic fluid in humans. It reduces the estradiol secretion by antral follicles (Gregoraszczuk and Ptak, 2013). It is also reported that exposure to PCB may reduce the anti-Müllerian hormone concentrations, and interfere with the oocyte quality, fertilization, implantation, and embryo quality (Karwacka et al., 2019; Meeker et al., 2011). It is also reported that serum concentration of PCB is associated with failed embryo implantation in women undergoing IVF.
BPA and Phthalates
BPA is present in many widely used daily consumer products such as plastic bottles, canned food, and receipt paper. It is the most common form of polycarbonate which has detrimental effects on reproductive health. Phthalates are mainly used as plasticizers in polyvinyl chloride (PVC) products and are classified as highly toxic substances based on animal reproduction studies (Ventrice et al., 2013). Phthalates are present in plastic food containers, plastic wraps, fragrances, and cosmetics. Plastic containers have been used for over 50 years as they are unbreakable. Both BPA and phthalate do not establish stable and irreversible bonds with the materials in which they are embedded. Therefore, they can leak easily from the plastic matrices and mix into food and drinks. This leaking is further increased when food is heated in the microwave. Therefore, these toxicants enter the human body through ingestion of contaminated water and food (Heudorf et al., 2007). Phthalates and BPAs through different mechanisms of hydrolysis, oxidation, and conjugation with hydrophilic molecules can migrate to many organs and are excreted through kidneys (Lovekamp-Swan and Davis, 2003; Thayer et al., 2015; Ventrice et al., 2013). Based on animal studies, dibenzyl phthalate (DBZP), diethylhexyl phthalate (DEHP), and dimethyl phthalate (DMPH) are classified as highly toxic by Registration, Evaluation, Authorization and Restriction of Chemical substances (REACH) (Ventrice et al., 2013). In the animal study (Rodent), DEHP seems to affect all steps of follicle development from pre-granulosa cell formation to ovulation. Exposure to DEHP during foetal life induces a significant decrease in oocyte number, interferes with meiotic progression, and abnormal activation and depletion of the resting follicular pool by increasing ROS levels (Zhang et al., 2016). In ART, the effects of phthalate and BPA are different. While a high urinary level of phthalate is associated with a higher risk of implantation failure in IVF, a high BPA level is associated with decreased antral follicle count and the number of oocytes (Sifakis et al., 2017). By hormonal dysregulation and interference of oogenesis and implantation, both phthalate and BPA lead to varying degrees of infertility (Patel et al., 2015). Moreover, BPA has a possible link to the pathogenesis of endometriosis and polycystic ovarian syndrome (PCOS) both of which have a tremendous negative impact on fertility (Hu et al., 2018); Palioura et al., 2015; Sifakis et al., 2017; Soave et al., 2020). There is a strong relation between continuous exposure to toxicants over time with poor functionality of the reproductive tract (Paoli et al., 2020). A higher level of BPA is also associated with miscarriage (Lenie et al., 2008), lower birth weight, and smaller head circumference in infants (Mok-Lin et al., 2010).
Climate change
Global climate change is mainly produced by greenhouse gas (GHG) emissions that are the consequence of warming of the atmosphere (IPCC Intergovermental Panel on Climate Change, 2013). The concentration of atmospheric CO2 ranges from 400 to 480ppm according to the IPCC (Intergovernmental Panel on Climate Change) projections in the year 2030 (Masson-Delmotte et al., 2018). Human-induced warming reached approximately 1∘C (0.8∘C to 1.2∘C) above preindustrial levels in 2017 and the increment of the temperature is at the rate of 0.2∘C per decade. Global warming of 1.5∘C is the global average safe surface temperature, which in certain regions of the world exceeds and is detrimental to humans and animals (Masson-Delmotte et al., 2018). Reproduction can be affected directly by extremes of effective ambient temperature (EAT) and indirectly by climatic changes. For example, extremely cold or hot environments alter normal maintenance requirements, because homeostasis is disrupted beyond the range of thermoneutrality. Disturbances of homeostasis then can alter reproductive function. Heat stress changes the luteal phase and ovulation in humans (Carpenter and Nunneley, 1988). Animal studies reported that heat stress or high environmental temperature has adverse effects on the reproductive and biological functions of dairy animals (Sere et al., 2008). Many climatic factors, like temperature, humidity, radiation, and wind velocity, affect animals’ environment directly or indirectly (Gwazdauskas, 1985). High ambient temperature is a major contributing factor to reducing fertility and lactation in cows (De Rensis et al., 2003; Dash et al., 2016). Heat stress causes a 20% to 30% reduction in conception rate (Khan et al., 2013; Schuller et al., 2014), affects oocyte growth and quality in cows and pigs (Barati et al., 2008; Ronchi et al., 2001), impairs embryo development, hence reducing pregnancy rate (Hansen, 2007; Wolfenson et al., 2000). Animal studies showed that the decline of conception has been associated with elevated rectal (Monty and Garbareno, 1978; Stott and Wiersma, 1976; Turner, 1982; Zakari et al., 1981) and uterine (Gwazdauskas et al., 1973) temperatures. Ulberg and Burfening (1967) found that pregnancy rates declined from 61% to 45% as rectal temperatures at 12h postbreeding increased by 1∘C. Cattle exposed to 32.2∘C ambient temperature for 72h after insemination and rectal temperatures of 40.0∘C had 0% conception compared with 48% conception when the rectal temperature was 38.5∘C and ambient temperature was 21.1∘C (Dunlap and Vincent, 1971). Direct effects of hyperthermia on the survival of early zygotes and embryos also have been postulated (Alliston et al., 1965; Burfening and Ulberg, 1968; Dunlap and Vincent, 1971; Gwazdauskas et al., 1981; Stevenson et al., 1988; Ulberg and Burfening, 1967). Lenz et al. (1983) reported that the portion of oocytes that progress to Metaphase II was reduced as the temperature increased from 35∘C to 39∘C to 41∘C.
Steroid production is strongly affected by seasonal variation (Hozyen et al., 2016; Zhang et al., 2020; Zheng et al., 2020). The heat stress causes the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary which triggers the release of cortisol and other glucocorticoids from the adrenal cortex. Luteinizing hormone is inhibited by the secretion of glucocorticoids. High ambient temperature or thermal stress can affect the endocrine system during the dry period that may shorten the gestational length, increase fetal abortions, lower birth weight, and reduce follicle and oocyte maturation. During summer, progesterone level in follicular fluid and blood is significantly reduced resulting in a higher incidence of preimplantation embryonic death (Matsuzuka et al., 2005). Animal studies showed that farm animals exposed to high temperatures have a high level of DNA damage and apoptosis. Oocyte exposure to high temperatures at birth resulted in increased oocyte loss early in life (Boland et al., 2015; Edwards and Hansen, 1997; Hansen, 2015; Kemkes, 2010). This reduction in oocyte numbers thereby reduces a woman’s reproductive life due to loss of the follicular pool. The same was opined by researchers of Austria (Huber et al., 2004), New Zealand (Huber et al., 2008), and New York City (Boland et al., 2015). However, other studies reported increased fertility in women born in an environment with high temperatures (Huber and Fieder, 2009, 2011). Very recently, Gaskin et al. (2021) described that a 1∘C increment of temperature was associated with a −1.6% lower AFC. They concluded that exposure to higher temperatures was associated with a lower ovarian reserve and this raising ambient temperature may result in accelerated reproductive ageing of women worldwide (Gaskin et al., 2021).
Is there any solution?
The consequences of today’s environmental pollution are not easy to fix. This pollution is an overall effect of growing populations worldwide and their needs. Steps should be taken to minimize the use of chemicals, plastics, and pesticides which have adverse effect on reproduction.
Women of reproductive age and young children should avoid fish with high mercury content like mackerel, shark, swordfish, marlin, tilefish, and tuna (Stern and Smith, 2003). US Environmental Protection Agency recommends seafood and fish low in mercury like shrimp, salmon, pollock, and catfish. They should avoid using imported skin creams which are high in lead, and avoid cooking with lead-glazed pottery. If there is a suspected toxic lead level >20μgm/dl, chelation therapy may be needed (Schnaas et al., 2006). If the patients are living near an active mining, smelting, or industrial area, they may have an increased risk of exposure to smoke. Using HEPA in the working zone for clean air can be a good alternative. Smoking either active or passive should be prohibited. Women who are trying to conceive should be encouraged to have organic rice and organic products. To reduce pesticide exposure, women are encouraged to eat organic fruits and vegetables. People working in agriculture should wash their hands after work, wear appropriate protective gear, and remove their shoes before entering the house (Thalia and Giudice, 2019). To minimize the EDs toxication, people should limit the use of plastic containers, especially reheating in microwave, and are advised to switch from plastic containers to glass and stainless steel. The couple should be encouraged to cook at home and avoid or limit the use of fast food, canned foods, and processed foods. People should avoid bottled water with the number 7 stamped on the bottom (Thalia and Giudice, 2019). To reduce the effect of global warming, the source of CO2 emissions should be reduced. Limiting warming to 1.5∘C implies reaching net-zero CO2 emissions globally around 2050 and concurrent deep reductions in emissions of non-CO2 forcers, particularly methane (Masson-Delmotte et al., 2018). It can be done by reducing energy demand, decarbonization of electricity and other fuels, electrification of energy end-use, deep reductions in agricultural emissions, and some form of CDR (Carbon Dioxide Remover) with carbon storage on land or sequestration in geological reservoirs. Proper education and awareness should be encouraged as much as possible.
CONCLUSION
With the passage of time, environmental pollution and climate change are significantly increasing day by day. Consequently, there is a significant increase in infertility due to a reduction in sperm and ovum count and quality. Moreover, prolonged exposure to environmental pollution and climate changes may cause pregnancy losses, birth defects, and postnatal abnormal neurodevelopment. Individual environmental agents have their own individual adverse effects; however, women are exposed to a complex mixture of environmental chemicals which affect multiple sites of reproduction. Although the consequences of environmental pollution on human health are still a matter of debate, large-scale multinational studies are required to establish the cause and effect relationship.
CONFLICT OF INTEREST
There is no conflict of interest.