Effects Of Lead On Reproductive Functions

June 27, 2018

By Professor of Anatomy/Consultant Reproductive Endocrinologist
dapo.ashiru@medicalartcenter.com 0700 MARTCENTERRecently, Sheryl Vanderpool of the World Health Organisation circulated a paper to the 15th-member FIGO working committee on Reproductive Toxins with a special request that we spread the information contained therein widely.

I, therefore, wish to use this article to highlight the points raised in the paper titled, ‘Toxic Truth: Lead and Fertility by Karen Clay,’ Heinz College Carnegie Mellon University and her group from the National Bureau of Economic Research in Cambridge USA – Working Paper 24607 http://www.nber.org/papers/w24607, May 2018.

Here is an excerpt from the paper: Using U.S county-level data on lead in the air for 1978-1988 and lead in topsoil in the 2000s, this paper examines the impact of lead exposure on a critical human function with societal implications – fertility.

To provide causal estimates of the effect of lead on fertility, we use two sets of instruments: (i) the interaction of the timing of implementation of Clean Air Act regulations and the 1944 Interstate Highway System Plan for the panel data and (ii) the 1944 Interstate Highway System Plan for the cross-sectional data.

We found that reductions in the airborne lead between 1978 and 1988 increased fertility rates and that higher lead in topsoil decreased fertility rates in the 2000s. The latter finding is particularly instructive, because it suggests that lead may continue to impair fertility today, both in the United States and in other countries that have significant amounts of lead in topsoil.

We in Nigeria must find this to be alarming. One cannot overemphasise the detrimental role that toxins play not only in the development of certain ailments like cancers and pulmonary pathologies but also on our reproductive health. Current experience in clinical practice amplifies this hazard, and it is particularly worrisome because there is no robust programme in our country that deals with the estimation or control of the various toxins released into the environment.

Environmental toxins come in various forms like fumes from automobile and generator exhaust, diesel engines, industrial waste, etc. As a result, there is substantial cross-sectional variation in the lead in topsoil. Lead in topsoil is re-suspended in a number of contexts, including dry or windy seasons, during construction, and when it is tracked into houses in the form of dust.

For both airborne lead and lead in topsoil, exposure occurs through inhalation and consumption. Consumption occurs when food or drink comes in contact with dust or if food is grown in lead-contaminated soil. In 2010, the World Health Organisation stated that for the general population, “the largest contribution to the daily intake of lead is derived from the ingestion of food, dirt, and dust.” (WHO 2010).

Fertility is important at both the individual and societal levels, where it has implications for economic activity. Thus, factors that adversely affect fertility are of significant policy concern. Animal studies and epidemiological research on workers with high occupational exposure have shown that lead can adversely affect both male and female reproductive systems, whether these effects extend to fertility in the broader population, where exposure levels are lower, and the magnitude of any causal effects are open questions.

According to Clay et al. who used the U.S. county-level data on lead in the air for 1978-1988 and lead in topsoil in the 2000s for analysis, there is causal evidence on the effects of lead exposure on the general fertility rate.

Beginning in the 1920s, the lead was used as an anti-knock compound in gasoline and was emitted with other particulates from tailpipes. Airborne lead fell rapidly during 1978-1988, in part because of regulatory requirements governing lead in gasoline in the Clean Air Act. Lead in topsoil is the result of naturally occurring lead and long-term deposition of lead from a variety of anthropogenic sources including lead smelting, industrial activity, agricultural activity, electricity generation, lead in paint, and gasoline emissions.

In Nigeria, the situation also exists, perhaps to a greater degree. It is, therefore, a necessity for us to know more about the danger that lead can pose to personal health and potentially to generations yet unborn, as well as common routes of everyday exposure.

Lead in the Human Body

Lead primarily enters the body from breathing in dust or chemicals that contain lead or by ingesting food or liquids that contain lead. Once lead reaches the lungs, it goes quickly to other parts of the body via the bloodstream. When the lead reaches the stomach, some of it is further absorbed into the bloodstream and the remainder is excreted.

Once in the blood, lead travels to the soft tissues and organs such as the liver, kidneys, lungs, brain, spleen, muscles, and heart. After several weeks, most of the lead moves into the bones and teeth. The half-life of lead in blood is approximately 30 days.

Once it is taken in and distributed to organs, the lead that is not stored in bones leaves the body via urine or feces. The primary method for determining lead exposure is a measurement of blood lead levels.

Although the public discussion has focused on the effects of lead in children, adults are also adversely affected by lead. The focus on young children has been driven by the effects of lead on neurological development, which has implications for IQ, educational outcomes, and behavioral outcomes.

According to the Centers for Disease Control and Prevention (CDC 2017), The National Toxicology Program (NTP 2012), and the American Academy of Pediatrics (AAP 2016), there is sufficient evidence to state that there are adverse health effects in children and adults at blood lead levels (BLLs) <5 micrograms per deciliter (μg/dL). Adults can experience a variety of adverse health effects including decreased renal function, high blood pressure, hypertension, and infertility.

Vectors of Exposure

Lead exposure occurs through a number of channels including air, water, food, paint, and soil. Airborne emissions are driven by industrial activities, coal-fired power plants, and on-road vehicles and small aircraft. Emissions from on-road vehicles were by far the largest source of lead emissions through 1996 but reached zero in 2002. Lead has not yet been banned in aviation gas (non-road engines) used for small aircraft. In 2011 it was the largest source of airborne lead emissions.

…to be continued

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