Fact sheet on lead and cancer

By Subothini Srikaran, Volunteer Researcher for the Global Lead Advice and Support Service

What is lead?

Lead is a main-group element (known to occur in nature) with an atomic number eighty two and the symbol Pb. It is one of the “heavy metals” (of high relative atomic mass), is one of the softest and weakest of the commonly used metals, is a poor conductor of electricity, has a low melting point and resists acid corrosion. Its colour is variable. For instance, when it is freshly cut, it has a bluish-white colour; on exposure to air it has a dull, greyish colour, and when it is melted into a liquid has a shiny chrome-silver lustre. ⁽¹⁾

Background on Cancer

Cancer, also known as malignant neoplasm, is a group of diseases where a class of cells shows uncontrolled growth, invasion and sometimes metastasis (spread to other sites in the body). In contrast, benign tumours are self-limited which do not invade or metastasize. ⁽²⁾

Association between lead exposure and cancer

According to Lundstrom et al, lead exposure expressed as three different indices was not recognized as a risk factor for lung cancer. The studies of lead-exposed workers referred to in this article illustrate different findings concerning the development of lung cancer. Mainly, the elevated incidences of lung cancer in lead smelter and battery workers are moderate and could be explained by confounding factors not accounted for. Some studies are limited by small number of participants. Most of the studies are complex because of multifactorial exposure and due to deficiency of detailed information about individual exposure to lead and to other exposures in the working environment. Most of the studies also lack information regarding dietary and smoking habits. Furthermore, five other studies have not demonstrated elevated risks for any malignancies in lead-exposed workers. Authors of this paper conclude that, according to the findings in previous studies and their nested case-referent study, there is insufficient evidence to support occupational exposure to inorganic lead and lead compounds as a possible risk of lung cancer in humans. ⁽³⁾

Wong et al found a significant mortality from stomach cancer in the cohort study. However, the elevation of stomach cancer mortality derived from the analyses of the cohort and the nested case control study did not seem to be related to lead exposure. Wong et al also observed a small, statistically significant mortality increase from lung cancer. However, they suggest that the small increase- in the absence of an exposure response relationship - could be because of confounding as a result of smoking, and probably not causally related to lead exposure. Although there was a significant increase in the cancer of the thyroid and other endocrine glands, few deaths, deficiency of data about potential confounding factors, and the deficiency of reporting of a similar elevation in other studies highlight the requirement to perceive this finding carefully. In addition, they did not find an increase in mortality from lung cancer, bladder cancer, cancer of the central nervous system or lymphatic and hematopoietic cancer.⁽⁴⁾

Steenland et al suggest that, according to animal studies, lead is not genotoxic invitro. However it is said to promote the mutagenicity of other mutagens, perhaps through inhibition of DNA repair. [A mutagen is also likely to act as a carcinogen: Hutchinson, Dictionary of Science, 1194]. For example, early animal studies have shown that lead causes cancer in animal studies, mainly kidney cancer in two species through various routes of administration. For instance, they found that lead acetate and lead oxide acted synergistically to elevate kidney and lung tumors respectively, after administration of known carcinogens (nitrosamines, benzo(a)pyrene.) ^{(5 & 6)}. Lead acetate was used in most of these studies because of ease of administration, given orally, subcutaneously, or intraperitoneally, generally at high doses. In contrast, most human exposure to lead is through lead oxides or inhalation of lead fumes. However, the compounds used in the aforementioned animal studies are all inorganic lead compounds, so if the blood lead level (in humans) is comparable to the levels in the studies then we could extrapolate these findings to humans. The authors suggest that in the eight studies with high exposures the evidence is rather indicative of a link with lung cancer and stomach cancer, but remains restricted. Perhaps confounding by arsenic is a concern in the study with the highest lung cancer relative risk. Also, there is weaker evidence of an association with kidney cancer and gliomas ⁽⁷⁾. 

 “There is some evidence showing that lead may cause cancer, but this evidence is weak. Most of the evidence linking lead exposure and cancer comes from studies of workers with high levels of occupational (work-related) exposure to inorganic lead. People who have worked in heavily lead-exposed industries have been found to have blood lead concentrations of 40 to 100 micrograms per deciliter (µg/dL). In comparison, in 1991, the average blood lead concentration in US males in the general population was 4 µg/dL (10 µg/dL is considered a low lead level).”

“A recent report in the literature suggested a link between occupational exposure to lead and brain cancer.”

REFERENCES:

1. American Cancer Society, “Lead: What Is Lead? How Are People Exposed to Lead? Occupations With Exposure To Lead. Does Lead Cause Cancer? What Do Scientific Studies Show? What Do Animal Studies Show? What Do the Expert Agencies Say? Does Lead Cause Any Other Health Problems?” American Cancer Society www.cancer.org/docroot/PED/content/PED_1_3X_Lead.asp
2. Wikipedia, Lead , Viewed on 15/02/2010.
3. Wikipedia, Cancer, Viewed on 15/02/2010.
4. Nils-Go¨ ran Lundstrom, Vagn Englyst, Lars Gerhardsson, Taiyi Jin, Gunnar Nordberg, Lung Cancer Development in Primary Smelter Workers: A Nested Case-Referent Study, J Occup Environ Med. 2006;48:376–380.
5. Otto Wong, and Fran Harris, Cancer Mortality Study of Employees at Lead Battery Plants and Lead Smelters, 1947-1995, American Journal Of Industrial Medicine, 2000, Volume 38, pp 255-270.
6. Kyle Steenland and Paolo Boffetta, Lead and Cancer in Humans: Where Are We Now? American  Journal Of Industrial Medicine, 2000, Volume 38, pp 295-299.
7. Thuy V. Lam, Pamela Agovino, Xiaoling Niu, Lisa Roché, Linkage study of cancer risk among lead-exposed workers in New Jersey, Science of the Total Environment, 2007, Volume 372, pp 455–462.
8. Steenland et al (2000).