Pesticide Residues in Man - Pesticides: Evaluation of Environmental Pollution - page 501

In recent years, there has been an increase in public concern that chronic low-
level exposure to pesticide residues in food and water might pose a serious cancer
risk to the general population (Hodgson and Levi 1996). Recent reports suggested
an association between exposure to pesticides and different types of human can-
cer (Amaral Mendes 2002; Safi 2002). While epidemiological studies have often
implicated pesticides as causative agents in human cancer (Blair et al. 1993), it has
usually been at a marginal level of significance. It is suspected that DDT and its
breakdown product DDE, persisting in the environment long after being banned,
may be involved in the causation of breast cancer as a result of estrogenic activity
(e.g., Krieger et al. 1994). In his study on the association between chronic expo-
sure to pesticides and recorded cases of human malignancy, Safi (2002) reported
that heavy use and misuse of pesticides and other toxic substances in the Gaza
(Palestine) environment are suspected to be correlated with the growing incidence
of cancer. Higher level of OCPs, especially β-HCH, γ-HCH, and p,p′-DDE, might be
associated with prostate cancer risk (Kumar et al. 2010). How pesticides increase
these cancer risks is not thoroughly understood. Only about eight pesticides are
judged likely to be direct carcinogens by the International Agency for Research
on Cancer (IARC) (Vainio et al. 1994). However, some carcinogenic agents activate
cancers indirectly by altering the genetic materials of cells, disrupting cell divi-
sion, and inducing chromosomal damage in the lymphocytes (Cuneo et al. 1992;
Garry et al. 1992). In 1993, Pesticides News listed 70 possible carcinogens—now the
list has grown to over 160. Many of the pesticides included are obsolete chemicals
but may be found in stockpiles. Other pesticides are still in use, especially those
listed by the US EPA (PAN 2001).
iii. Hematopoietic cancers : Hematopoiesis is the formation of blood cellular components
from the hematopoietic stem cells located in the bone marrow. This process has a
very high level of continuous replacement of specialized cells. This implies that a
tremendous number of mitoses occur and there is an increased risk of mutations.
The bone marrow also contains fat tissues that have a high storage capacity and
may accumulate lipophilic compounds resulting in continuous exposure of hema-
topoietic progenitors and dendritic cells to xenobiotics. Hardell and coworkers
were among the first to propose a link between exposure to phenoxy herbicides
and the emergence of lymphoma (Hardell 1993). Thereafter, many epidemiologi-
cal studies were conducted in populations exposed to pesticides. Although a clear
correlation has been established between the agricultural practices and the occur-
rence of hematological malignancies (Alavanja et al. 2004), a specific link with the
use of pesticides is not always observed. Nevertheless, in a recent meta-analysis,
Merhi et al. (2010) showed a significant relationship between the professional expo-
sure to pesticides and the risk of developing hematopoietic malignancies, particu-
larly NHL. In AML (acute myeloid leukemia) patients professionally exposed to
pesticides or organic solvents, the clinicobiologic characteristics are similar to the
features of AML arising in patients with prior chemotherapy for another tumor,
thus suggesting that similar transformation pathways may underlie leukemogen-
esis induced by cytotoxic drugs and by environmental exposure to certain pesti-
cides or organic solvents (Cuneo et al. 1992).
iii. Neurotoxicity : Because of the basic similarities between the mammalian and
the insect nervous systems, the insecticides designed to attack the insect ner-
vous system are capable of producing acute and chronic neurotoxic effects