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Environmental factor, barrier 2 of 9

Lead and toxic chemicals

Lead and other toxic chemicals damage brain development, and no safe level of lead is known.

Evidence

  • No known safe level. Lanphear et al. (2005) pooled data on 1,333 children. Raising blood lead from 2.4 to 30 µg/dL was linked to a loss of 6.9 IQ points, with greater harm per unit at lower levels.
  • U.S. legacy exposure. McFarland, Hauer, and Reuben (2022) estimated over 170 million Americans alive today had high early-childhood lead exposure, mostly from leaded gasoline, costing about 824 million IQ points as of 2015.
  • Global burden. Larsen and Sánchez-Triana (2023) estimated for 2019: 765 million IQ points lost in children under 5, about 5.5 million adult cardiovascular deaths, over 90% of harm in low- and middle-income countries, and a cost of about US$6.0 trillion (roughly 6.9% of global GDP). These are model estimates with wide uncertainty.
  • All pollution combined. Fuller et al. (2022) found pollution causes about 9 million deaths per year, one in six worldwide. "Traditional" poverty-linked pollution deaths have fallen, while "modern" pollution deaths have risen over 66% since 2000.

Why it matters: Environmental factors often act through the other categories. Lead damages brain development (biological), poor families live nearer pollution (economic), illness reduces motivation (psychological), and weak institutions fail to regulate (societal).

Proposed and experimental methods

Methods that are proposed, under trial, approved in some places, or tried and then failed. Each shows a stage label and an evidence rating. A stage label shows how far a method has progressed, not whether it works. The stage labels are explained on the environmental factor page.

  • Mandatory lead service line replacement (Approved but not scaled, B). The U.S. Lead and Copper Rule Improvements, finalized in October 2024, require water systems to identify and replace lead pipes within 10 years, and EPA estimates benefits up to 13 times the costs (EPA, 2024). In 2026 the new administration said it would defend the 10-year deadline in court against a utility industry challenge, while lowering the estimate of remaining lead pipes from about 9 million to about 4 million, mainly through changes in method (Associated Press, 2026).
  • Enforcement against lead-adulterated spices (Early trial, C). In Bangladesh, turmeric was colored with lead chromate pigment. A 2017 to 2021 effort combined media coverage of the research, public notices, and food safety raids using rapid lead tests, after which detectable lead in market turmeric samples fell from 47% to 0% and the median blood lead of 15 mill workers fell 30% (Forsyth et al., 2023). There was no comparison area. In a separate cluster randomized trial, community health worker sessions raised lead awareness by 52 percentage points and increased self-reported safe turmeric use (Jahir et al., 2021).
  • Campaigns for lead paint laws (Approved but not scaled, C). The Lead Exposure Elimination Project (LEEP) tests paint on sale and helps governments draft and enforce limits. Its own follow-up study in Malawi estimated that the market share of brands selling lead paint for homes fell from about 67% in 2021 to 24% in 2023 (LEEP, 2024). A funder interview reports that five countries introduced lead paint regulations in 2025, but all impact figures come from LEEP's own studies and enforcement is not described (Gertler, 2026).
  • Reversed: Part of the U.S. limits on PFAS in drinking water (Failed or reversed, B). In April 2024 EPA set enforceable limits for six PFAS ("forever chemicals"), including 4.0 parts per trillion for PFOA and PFOS, with compliance by 2029. In May 2026 EPA proposed rescinding the limits for PFHxS, PFNA, HFPO-DA (GenX), and the mixture standard, and letting systems request an extension to 2031 for PFOA and PFOS (EPA, 2026).
  • Failed: Chelation drugs for moderately lead-exposed children (Failed or reversed, B). In a placebo-controlled trial of 780 toddlers with blood lead of 20 to 44 μg per deciliter, the oral chelator succimer lowered blood lead by 4.5 μg per deciliter for about six months but did not improve cognition, behavior, or neuropsychological scores at 36 months (Rogan et al., 2001) or at age 7 (Dietrich et al., 2004). The authors concluded that preventing exposure is what matters.

Sources cited on this page

  1. Lanphear, B. P., et al. (2005). Low-level environmental lead exposure and children's intellectual function. Environmental Health Perspectives, 113(7), 894-899. DOI B Moderate
  2. McFarland, M. J., Hauer, M. E., & Reuben, A. (2022). Half of US population exposed to adverse lead levels in early childhood. PNAS, 119(11), e2118631119. DOI C Limited
  3. Larsen, B., & Sánchez-Triana, E. (2023). Global health burden and cost of lead exposure in children and adults. Lancet Planetary Health, 7(10), e831-e840. DOI00166-3) C Limited
  4. Fuller, R., et al. (2022). Pollution and health: a progress update. Lancet Planetary Health, 6(6), e535-e547. DOI00090-0) C Limited
  5. Ma, L., Graham, D. J., & Stettler, M. E. J. (2021). Has the ultra low emission zone in London improved air quality? Environmental Research Letters, 16, 124001. link B Moderate
  6. Dietrich, K. N., Ware, J. H., Salganik, M., Radcliffe, J., Rogan, W. J., Rhoads, G. G., et al. (2004). Effect of chelation therapy on the neuropsychological and behavioral development of lead-exposed children after school entry. Pediatrics, 114(1), 19-26. link B Moderate
  7. Forsyth, J. E., Baker, M., Nurunnahar, S., Islam, S., Islam, M. S., Islam, T., et al. (2023). Food safety policy enforcement and associated actions reduce lead chromate adulteration in turmeric across Bangladesh. Environmental Research, 232, 116328. link C Limited
  8. Gertler, A. (2026, February 10). How LEEP is eliminating lead paint, one country at a time. Coefficient Giving. link C Limited
  9. Jahir, T., Pitchik, H. O., Rahman, M., Sultana, J., Shoab, A. K. M., Nurul Huda, T. M., et al. (2021). Making the invisible visible: Developing and evaluating an intervention to raise awareness and reduce lead exposure among children and their caregivers in rural Bangladesh. Environmental Research, 199, 111292. link B Moderate
  10. Rogan, W. J., Dietrich, K. N., Ware, J. H., Dockery, D. W., Salganik, M., Radcliffe, J., et al. (2001). The effect of chelation therapy with succimer on neuropsychological development in children exposed to lead. New England Journal of Medicine, 344(19), 1421-1426. link B Moderate

Every source for this factor is listed on the environmental factor page.