RESIDENTIAL PESTICIDES AND CHILDHOOD LEUKEMIA: A SYSTEMATIC REVIEW AND META-ANALYSIS. Turner M.C., Wigle, D.T. and Krewski, D.

Environmental Health Perspectives. 118(1):33-41 (2010) http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.0900966

This study concludes there is a positive association between residential pesticide (including both insecticides and herbicides) exposure during three critical windows, namely preconception, pregnancy, and childhood, with the subsequent development of childhood leukemia. The strongest link was shown with exposure to insecticides.

This systematic review recommends continued examination to elucidate "potential mechanics of action and pesticide interactions."  According to the authors, there is also a need to study the uses of pesticides indoors which are currently not addressed in Canadian cosmetic pesticide by-laws.

CHILDHOOD LEUKEMIA

Introduction/Definition: According to the Mayo Clinic, “leukemia is cancer of the body’s blood forming tissues, including the bone marrow and the lymphatic system.” According to the National Cancer Institute (NCI), in 2009 there were 44,790 new cases of leukemia; 21,870 deaths from leukemia occurred. According to the NH Department of Health and Human Services, leukemia accounts for 19% of all childhood cancer incidences.

Source: http://www.mayoclinic.com/

http://www.cancer.gov/cancertopics/types/leukemia

http://www.dhhs.nh.gov/dphs/hsdm/cancer/documents/childhood.pdf

There are many types of leukemia, some of which are more prevalent in children; other types are most likely to occur in the adult population. Leukemia can be either acute or chronic; it is classified by the speed of its progression as an illness and also by which cells are involved. There are four common types of leukemia: Acute lymphocytic leukemia (ALL); Chronic lymphocytic leukemia (CLL); Acute myelogenous leukemia (AML); and Chronic myelogenous leukemia (CML).

In general, leukemia is best characterized by an increase in white blood cells, called leukocytes, which are produced in the bone marrow (the soft, inner part of a bone cavity). Leukocytes are formed in the bone marrow; they defend the body against infection from both viruses and bacteria.

Leukemia occurs when some blood cells acquire mutations in their genetic makeup or DNA – it is here where each cell receives its instructions to perform certain actions. Mutations are alterations in genes or chromosomes which alter a cell’s character, in other words genetic change. It is these mutations that cause cells to grow and to divide rapidly and also to continue to do so when otherwise they would usually cease replicating. Thus, these cells are both damaged and immature. With this increase of cells, these abnormal cells dominate and crowd normal healthy oxygen carrying red blood cells (erythrocytes), blood clotting cells (platelets) and other normal white blood cells, (leukocytes). If untreated, these abnormal white blood cells overwhelm and invade the body’s tissues. This accumulation of damaged leukemic cells, in turn, causes the common signs and expected symptoms associated with leukemia like fatigue and weight loss.

Prevalence: In both the United States and Canada, leukemia is the most common form of cancer in children. In fact, the most common form of leukemia that strikes children is acute lymphocytic leukemia (ALL).

Causes: It is agreed that leukemia has a variety of causes, including environmental toxins such as exposure to pesticides. It is believed that pesticides cause genetic damage which, in turn, can contribute to the formation of cancer.

Let’s see how this can occur. According to Healthcommunities.com: all cancers begin as a mutation (loss or damage) in a cell’s DNA (genetic material). These changes or mutations occur over a person’s lifetime. These changes are copied and inherited by future generation of cells.

Specific errors within the DNA can take place. One change is called a translocation. A translocation means there is a transfer (a shift or displacement) of a segment of a chromosome on the same chromosome or to a different one. This can affect the normal sequencing of genes, whereby cancer promoting genes, called oncogenes might be “switched on” while cancer-preventing genes, tumor suppressors, might be summarily turned off. Some forms of leukemia exhibit these translocations which affect the chromosome of blood cells. 

Source:  http://www.oncologychannel.com/leukemias/causes.shtml

Risk Factors: Many risk factors may contribute to DNA damage within blood cells, including age, ethnicity, radiation, chemicals (pesticides), viruses, certain blood disorders, family history of leukemia, and genetic diseases (For example: the risk for developing leukemia is increased 15-fold for children with Down’s syndrome).

Articles cited: In the subsection titled Childhood Leukemia, we have provided summaries from research studies that clearly indicate that household pesticide exposure is a risk factor for the development of childhood acute leukemia. This increased risk is highly statistically significant especially in maternal occupational exposure.

Question: Why are children particularly susceptible or vulnerable to the dangerous effects of pesticides?

[1] Since a growing child’s internal organs are immature, three systems (enzymatic, metabolic, and immune) afford less natural protection compared to an adult.

[2] Human development has certain milestones or what are called “critical periods,” and it is thought that exposures at these junctions can permanently change or alter the way a child will develop and function.

[3] Since children ingest more food and drink as a percentage of their body mass than do adults, pesticide exposure is greater and has a more significant impact.

[4] Children are more likely to come into direct contact with pesticides due to recreational activities on grass and playing fields (major sources of exposure for children). Likewise, exposure is enhanced by the hand-to-mouth behavior frequent in young children.

Source:http://www.refuseotusechemlawn.org/health_effects.

Prevention:How can we prevent leukemia? We don’t have all the answers.  But, since we control the use of pesticides in our environment, a reduction in the use and exposure to pesticides could help.

HOUSEHOLD EXPOSURE TO PESTICIDES AND RISK OF CHILDHOOD ACUTE LEUKEMIA. Menegaux F. et al.,

Occupational And Environmental Medicine, 63(2):131-134 (2006) http://www.ncbi.nlm.nih.gov/pubmed/16421392

The data from this study suggests certain types of residential insecticide exposure are associated with an increased risk of acute childhood leukemia, especially during pregnancy. The same holds true for the use of both insecticides and fungicides used in the garden although the risk is not as significant. Also, exposure to insecticidal shampoos (which contain a variety of insecticides) to treat head lice is associated with acute childhood leukemia, and should therefore be investigated.

CRITICAL WINDOW OF EXPOSURE TO HOUSEHOLD PETICIDES AND RISK OF CHILDHOOD LEUKEMIA. Xiaomei Ma, et al.,

Environmental Health Perspectives. 110(9):955-960 (2002) http://ehp03.niehs.nih.gov/article/info%3Adoi%2F10.1289%2Fehp.02110955

The data from this study suggests that household pesticide exposure is associated with an increased risk of childhood leukemia. Households that employed professional pest control services before birth and up to three years showed a significant increased risk for childhood leukemia. Professional pest control services included “insect repellents, and the use of various products to control ants, flies, cockroaches, spiders, termites, and plant/tree insects.” Moreover, the highest risk was demonstrated during the second year of exposure. Furthermore, early exposure (three months before attaining pregnancy, being pregnant, and the first three years of life) to insecticides appears to be more harmful than exposure later in life. In addition, the more frequent the exposure (i.e. dose response relationship), the greater the associated risk to develop leukemia.

This study recommends further analysis of household pesticide exposure as it relates to childhood leukemia, the etiology of which will be better understood when the timing and location of the pesticide exposure is given more weight as a credible risk factor.

CHILDHOOD LEUKEMIA AND PARENTS’ OCCUPATIONAL AND HOME EXPOSURES. Lowengart, R.A., et al.,

Journal of the National Cancer Institute, 79: 39, (1987) http://www.ncbi.nlm.nih.gov/pubmed/3474448

This case control study was conducted on children under the age of ten to investigate causes of childhood leukemia in Los Angeles County. Results conclude that a statistically significant “increased risk was found for children whose parents used pesticides in the home (OR = 3.8, P = .004) or garden (OR = 6.5, P = .007)”. This risk is also increased with frequent use.

CHILDHOOD LEUKEMIA AND PARENTAL OCCUPATIONAL EXPOSURE TO PESTICIDES: A SYSTEMATIC REVIEW AND META-ANALYSIS. Van Maele-Fabry G. et al.,

Cancer Causes Control, 21(6): 787-809 (2010) http://www.ncbi.nlm.nih.gov/pubmed/20467891

This concise systematic review recommends minimizing parental occupational exposure to pesticides. Researchers also recognize the need to study pesticide exposure in general. Additionally, this study states that the strongest evidence of an increased risk for childhood leukemia pertains to maternal pesticide occupational exposure.

A SYSTEMATIC REVIEW AND META-ANALYSIS OF CHILDHOOD LEUKEMIA AND PARENTAL OCCUPATIONAL PESTICIDE EXPOSURE. Wigle, D.T., Turner, M.C., and Krewski, D.

Environmental Health Perspectives, 117(10):1505-1513 (2009) http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.0900582

This concise review recommends additional study of pesticide exposure. Conclusive results were found linking child exposure to pesticides via parental occupation and leukemia, especial prenatal maternal exposure. This study also concludes that parental occupational exposure to pesticides also significantly affects fetal development.

RISK OF CHILDHOOD CANCERS ASSOCIATED WITH RESIDENCE IN AGRICULTURALLY INTENSE AREAS IN THE UNITED STATES. Carozza S et al.

Environmental Health Perspectives, 116(4):559-565 (2008) http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.9967

This joint study by three prestigious university public health and epidemiological centers and the National Center for Atmospheric Research indicates an alarming coincidence of childhood cancers due to pesticide drift caused by agricultural usage. The authors conclude that “results showed statistically significant increased risk estimates for many types of childhood cancers associated with residence at diagnosis in counties having a moderate to high level of agricultural activities.”

PESTICIDES AND CHILDHOOD CANCER: AN UPDATE OF ZAHM AND WARD’S 1998 REVIEW. Infante-Rivard, C., and Weichenthal, S.

Journal of Toxicology and Environmental Health, Part B, 10:81–99 (2007) http://www.ncbi.nlm.nih.gov/pubmed/18074305

This toxicological study indicates that children are notably at risk to pesticide exposure throughout gestation due to parental occupation and carry-home residues. It is an update of an important review of existing studies. The authors from McGill‘s Department of Epedmiology concluded the following. “A number of epidemiological studies consistently reported increased risks between pesticide exposures and childhood leukemia, brain cancer, neuroblastoma, non-Hodgkin's lymphoma, Wilms' tumor, and Ewing's sarcoma.”

NEOPLASTIC RESPONSE OF MOUSE TISSUES DURING PERINATAL AGE PERIODS AND ITS SIGNIFICANCE IN CHEMICAL CARCINOGENESIS. Vasselinovitch, S. et al.,

Perinatal Carcinogenesis, 51 (1979) http://www.ncbi.nlm.nih.gov/pubmed/384263

A series of studies pertaining to perinatal carcinogenesis have been reviewed for this report. The authors’ main objective was development and definition of a sensitivity biologic model for carcinogenicity screening. Tumor response of mice treated during specific perinatal age periods with DEN, BP, aflatoxin B1, benzidine . 2HCl, DDT, dieldrin, and safrole were analyzed. The results revealed that the age of the animals at the time of carcinogenic exposure has been the most effective modulator of carcinogenesis in liver, lung, stomach, ovary, and lymphoreticular tissues.