Pollution and reproduction

The effects of pollution on reproduction are felt globally. Pollution significantly interferes with all aspects of sexual reproduction from male and female fertility to fetal development, birth outcomes, and long-term health of offspring. The risk of adverse birth outcomes such as miscarriage, stillbirth, preterm birth, low birth weight and birth defects increase when pregnant women are exposed to air pollution. The criteria air pollutants sulfur dioxide, nitrogen dioxide, particulate matter, carbon monoxide, ozone, and lead have been identified as harmful to human health by the World Health Organization and the U.S. Environmental Protection Agency (EPA) and are known to interfere with reproduction. Many of them are linked to the burning of fossil fuels, through vehicle use, heating and cooking. Indoor and outdoor air pollution can also contain endocrine-disrupting chemicals and microplastics that disrupt fertility, fetal development, and reproductive health. Pollutants can be inhaled, eaten, drunk, or absorbed through skin. Steps can be taken to minimize exposures such as avoiding smoking, minimizing dust, using glass instead of plastics, carefully selecting cleaning products and cosmetics, and exercising away from heavy traffic routes. Control strategies can also be implemented to improve industrial safety and public health. Cities such as London, Paris, Bogotá and Kraków have made changes that decrease pollution.

Demographics Total fertility rates (TFRs) have fallen globally in all recorded countries since the early 1960s. It has been argued that cultural and social factors are not sufficient to explain this global decrease. For example, fertility rates in China were already falling before the introduction of social campaigns such as the "later, longer, fewer" campaign (1973–1979) or the one-child-family policy (introduced in 1979). The United Nations reported in 2022 that two-thirds of the global population live in countries with fertility rates below replacement levels. The reduction in fertility rate over the last fifty years correlates with increasing global prosperity, but also with increasing environmental pollution. Given that all countries seem to be affected, it has been argued that environmental contamination may explain this widespread decline. Environmental contaminants have been shown to impact human fertility in a variety of ways. While populations worldwide are reporting lowered reproductive ability, marginalized communities and minorities tend to be exposed to higher levels of air pollutants than majority populations. They experience higher rates of adverse reproductive outcomes. The impact of race and ethnic group was examined in a data meta-analysis of perinatal outcomes from 53 high- and upper-middle-income countries. Black women were consistently at higher risk for adverse perinatal outcomes including neonatal death, stillbirth, preterm birth, and small-for-gestational-age babies compared to white women. South Asian women were also more likely to experience adverse outcomes such as preterm birth and small-for-gestational-age babies, irrespective of geographical region. Reproduction is increasingly being examined within a framework of environmental health and reproductive justice.

Pollutants Pollutants can be inhaled, eaten, drunk, or absorbed through skin, with inhalation being the most common means of exposure. Air pollution is a volatile mixture of both gases and particles whose components differ in terms of chemical reactivity, duration of exposure, and severity of effects. Pollutants can travel long distances, and mixtures of pollutants can vary widely across both space and time depending on factors such as pollution sources, geography, and season. Such differences can make it difficult to generalize across studies. Research done in different places or at different times may attribute the effects of pollution to different components based on the mixture of pollutants present. Measurement of individual components within mixtures and estimation of their causal effects are complicated by the presence and interactions of multiple components. In cases where a single pollutant is used as a proxy indicator for general levels of air pollution, observed effects may be misattributed to the measured pollutant, when unmeasured components of polluted air are actually responsible. Mixture analysis methods are used to measure and examine multiple components and better attribute the overall effects of air pollution to specific components. Research has consistently shown that exposure to pollutants can affect fertility, fetal development, health of offspring in later life, and the genetics of future generations. Potential mechanisms of action by toxic environmental chemicals include oxidative stress, inflammation, changes in placental function, endocrine disruption and genetic alterations.

Carbon monoxide Carbon monoxide (CO) is an odorless gas released by the burning of fossil fuels in fires, boilers and motor vehicle engines. CO is also released by biomass fueled-cooking and is found in firsthand and secondhand tobacco smoke. CO affects both outdoor and indoor air quality. CO from traffic-related air pollution is found in higher concentrations in areas of higher traffic volume and congestion, and in poorly ventilated traffic and parking areas. Carbon monoxide binds to hemoglobin in red blood cells, reduces the oxygen-carrying capacity of blood, and interferes with cellular respiration. It prevents delivery of oxygen to tissues and causes cellular and tissue damage. In cases of pregnancy, the effects of carbon monoxide poisoning are much greater and longer lasting on the fetus than on the pregnant woman.

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