Pesticide / insecticide exposure

Residents of a condominium or housing estate in Singapore scurry to close all their windows when they hear “Brrrrrr ….” outside their flat or house. This is the familiar sound of the machine which spews out a thick cloud of insecticide to kill mosquitoes or bugs in the compound. When the dense white cloud has dispersed, the air is still laced with the lingering smell of chemicals for some time. I have always wondered what health hazard this fogging / fumigation poses.

A recent article titled “Residential and childhood leukemia: A systematic review and meta-analysis” written by researchers from the University of Ottawa caught my eye (Environmental Health Perspectives 2010; 118: 33 – 41). They reviewed and analysed previously published epidemiological studies examining the relationship between residential pesticide exposure during critical exposure time windows (preconception, pregnancy and childhood) and childhood leukaemia. The analysis found a positive association of exposure and childhood leukaemia. During pregnancy, exposure to unspecified residential pesticides, insecticides and herbicides carried 54%, 105% and 61% increased risk of childhood leukaemia, respectively. During childhood, exposure to unspecified residential pesticides and insecticides carried 38% and 61% increased risk of childhood leukaemia, respectively.

Most childhood leukaemia occurs in the first few years of life. Most leukaemics carry gross chromosomal abnormalities in their blood. A study in the late 90s on routinely collected blood samples in neonates showed the presence of leukaemic clones with specific chromosomal translocations in children who later developed acute lymphoblastic leukaemia (ALL) [Proc Natl Acad Sci USA 1997; 94: 13950 -13954]. Another study suggested that pre-leukaemic clones may persist throughout childhood and may require post-natal exposure for leukaemic progression (Genes Chromosomes Cancer 2004; 39: 335 – 340). A recent study of infants born in an agricultural region in the Philippines showed that the prevalence of a common acute myologenous leukaemia (AML) translocation [t(8;21)] in cord blood samples was about doubled in those infants with detectable meconium levels of the methylcarbamate insecticide propoxur (Pediatr Blood Cancer 2007; 49: 624 – 628).

Leukaemia is the most common form of childhood cancer in Canada and the United States. ALL accounts for about 80% of childhood leukaemic cases. The next most common is AML. Although the precise mechanism on how leukaemia develops is still unclear, the two-step leukaemia model proposes that leukaemia development occurs after 2 mutations. The first mutation, usually a chromosomal translocation, occurs in utero. The second mutation, occurring after birth, completes the process and leukaemia occurs. While ionizing radiation is the only proven environmental risk factor to play a role in the etiology of leukaemia, other potential risk factors include parental smoking and alcohol consumption, electromagnetic field exposure, hydrocarbons, socioeconomic factors, immunity and infection and pesticides.

While it has not been convincingly proven that pesticides / insecticides cause leukaemia, it is probably no harm that we avoid unnecessary exposure to these substances as much as possible. While fogging / fumigation helps to reduce the mosquito population, it may bring nastier problems in its place to you and your family.