Impacts of benzene on public health
The Ministry of Health's acknowledgement of the highest benzene concentration ever recorded in Jamaica's air following the March 2015 fire at the Riverton dumpsite is only the tip of the iceberg.
The weak air-quality monitoring programme conducted by the National Environment and Planning Agency prevents the public from appreciating the real magnitude of Jamaica's environmental health problems, especially those related to poor solid-waste management. Air pollutants such as some of those from the 'Dirty Dozen' (dioxins, furans and PCBs), biphenol A and heavy metals are not measured, but they are more dangerous to health because they can accumulate in the body, especially in fatty and soft tissues.
Metals differ from other toxic substances in that they are neither created nor destroyed by humans. These pollutants will be dealt with in another article. This time, I will focus on benzene.
Background monitoring stations report concentrations of benzene from sources other than dump fires such as motor vehicle emissions, so the high-concentration event cannot be separated from the year-round low, but risky, benzene concentrations.
No safe exposure
The World Health Organization (WHO) considers benzene to be carcinogenic to humans. No safe level of exposure can be recommended. Using WHO estimates of the excess lifetime risk of leukaemia at an air concentration of 84 ug/m3, the estimate is 494 cases per million population.
Ontario regulations propose a 24-hour average standard of 2.3 mg/m3 for benzene based on the carcinogenic effects associated with exposure to benzene. The concentration of benzene at the Half-Way Tree Road background monitoring station was 7.87. Two weeks after the 2012 fire, the benzene concentration was 13. Therefore, background benzene concentrations in Jamaica EXCEED the Ontario standard. Jamaica does not have standards for benzene.
The risk of harmful health effects from toxic substances depends on many factors such as dose, health, age, adaptation, routes of exposure, frequency and duration of exposure (acute vs chronic).
Benzene is a carcinogen (causes cancer), mutagen (causes mutations in DNA), teratogen (causes birth defect), allergen (causes unnecessary immune response), neurotoxic (damages nervous system), and endocrine disruptor (interferes with hormones).
High concentrations of benzene cause the
following short-term effects: drowsiness, dizziness, rapid or irregular heartbeat, headache, tremors and confusion immediately after exposure to high levels of the substance.
Long-term exposure to benzene causes other health problems like aplastic anaemia, excessive bleeding,reduction in the capacity of the immune system to fight infections, cancers, and chromosomal aberrations in human peripheral lymphocytes.
Other studies have also found that
- Benzene crosses the placenta and is present in cord blood in concentrations equal to or greater than maternal blood.
- Women exposed to benzene concentrations of 2.86 to 7.44 ug/m3 had a 2.3 odd ratio of having a child with neural tube defect (spina bifida) and a 1.28 odd ratio for having a child with anencephaly (improper formation of the top part of the skull and brain).
- Early-life exposure to ambient air pollution may increase the risk of upper and lower respiratory tract infections in infants.
- Increase in preterm birth or a decrease in biparietal diameter growth with maternal exposure to benzene or early exposure to aromatic solvents. Biparietal diameter is one of the basic biometric parameters used to assess fetal size.
- Enzene is fetotoxic (causes mutations in DNA) in mice and rabbits following maternal exposure by inhalation, causing a reduction in birth weight.
- Results of animal studies showed that benzene may cause Zymbal-gland (ear canal) carcinoma, oral-cavity tumours, skin cancer, lymphoma, lung tumours, ovarian tumours, and mammary-gland carcinoma.
- Dr Homero Silva is professor in public health, environment and climate change at UTech's School of Public Health and Health Technology. Email feedback to firstname.lastname@example.org.