Texas watershed cancer link

segunda-feira, 29 de março de 2010

A study in the Journal of Water and Health examines a possible link between an increased risk of childhood cancer and the geographic location of the mother at birth. This increased risk was estimated for each watershed in Texas.

Although rare in terms of absolute numbers, cancer is the most common fatal disease among US children. The foetus has reduced resistance to toxic injury and is especially prone to mutagenic injury because of the high rate of cell division. A foetus can be exposed to environmental toxins through maternal consumption of contaminated water.

Non-point source (NPS) pollution is generally considered to be the major cause of water problems. Sources of non-point pollution include both agricultural and residential pesticides, toxic chemicals from urban runoff, heavy metals and acids from abandoned mines and atmospheric deposition. The authors attempt to determine how spatial patterns of toxin-induced disease, specifically childhood cancer, are correlated with spatial patterns of water contamination.

The authors describe how geographic modelling of rare diseases such as childhood cancer has been hampered by imprecise risk estimates. Previously, such investigations have focused on geopolitical boundaries or buffers around point sources and have reported inconsistent results. More direct exposure assessment is needed and should be focused on areas of higher risk. Once high-risk locations such as specific watersheds are identified, prospective studies will become feasible.

The authors created a database to evaluate the geographical risk of the mother’s living location at time of birth. Birth records from 1 January 1990 were retrieved from the Texas Department of State Health Services and all births were followed for cancer incidence as reported to the Texas Cancer Registry as of 1 January 2003. Cancer diagnoses were classified into 19 groups according to the International Classification of Childhood Cancers. The article describes the statistical modelling process and use of GIS in watershed identification.

By correlating the two databases, the authors identified 3718 incidences of cancer spread throughout the 19 histotype groups from a total of 3.8 million births. In order to identify high-risk locations, the study used the posterior likelihood of a relative risk greater than 1. A total of nine Texas watersheds were found to have higher than 90% posterior likelihood of an SMR (standardised morbidity ratio) greater than 1 for a childhood cancer histotype.

Watersheds in the Great Plains in North Texas (Lake Meredith (image), Upper Prairie Dog Town Fork Red, Middle Canadian-Spring, Upper North Fork Red, Upper Salt Fork Red and Middle North Fork Red) had high posterior likelihoods for increased risk of astrocytomas. GIS analysis showed that these watersheds were largely overlying the Ogallala aquifer. There are at least two suspected potential toxic exposures spread through the water in this location: pesticide applications in this largely agricultural area and drinking water contamination from the Federal superfund site.

In addition, two watersheds near Houston, Buffalo-San Jacinto and West Galveston Bay, had increased risk for renal cancer and acute lymphoid leukemia, respectively. A watershed in South Texas, the South Laguna Madre, also had increased risk for atypical leukemias.

The authors conclude that further research should address these location and cancer type correlations. Specifically, the possibility that waterborne toxins cause these childhood cancers should be investigated further.

Source: James A. Thompson, Susan E. Carozza, Wesley T. Bissett and Li Zhu, 2010. Risks of childhood cancer among Texas watersheds, based on mothers’ living locations at the time of birth. Journal of Water and Health (IWA Publishing ), 8(1), 139-146.