DDT exposure in early childhood and female breast cancer: Evidence from an ecological study in Taiwan

Researchers still lack consensus on the association between exposure to DDT and the risk of breast cancer. One reason could be that the measurements of DDT obtained during or near the time of diagnosis may not reflect exposure during the etiologically relevant time period in a woman's life. This study undertook an ecological analysis to investigate whether exposure to DDT among cohort born between 1951 and 1959 (i.e. age 0-5 years) and who reached the age 50-54 years during 2001-2013 had an increased risk of breast cancer in adulthood. To do this, we used the number of DDT sprays in each township during the anti-malaria campaign in Taiwan in the 1950s as a proxy for direct DDT exposure. The DDT sprays were then linked to the township female breast cancer incidence rate in the 2000s when the birth cohorts had reached age 50-54 years. Insurance claims data were used to identify breast cancer cases during 1996-2013. Zero-Inflated Poisson regression was performed to estimate the effect of DDT sprays on the breast cancer incidence rate. The analysis was based on a total of 9 birth cohorts (1951-1959) in 349 townships who had lived at least up to age 50. On average, one DDT spray experienced during age 0-5 years was associated with an increase of 8 more female breast cancer cases per 100,000 during age 50-54. The effect appears to increase with the number of sprays. Our finding suggests that DDT exposure in early childhood could raise the risk of breast cancer in adulthood.

Estimating Time-Varying PCB Exposures Using Person-Specific Predictions to Supplement Measured Values: A Comparison of Observed and Predicted Values in Two Cohorts of Norwegian Women

BACKGROUND

Studies on the health effects of polychlorinated biphenyls (PCBs) call for an understanding of past and present human exposure. Time-resolved mechanistic models may supplement information on concentrations in individuals obtained from measurements and/or statistical approaches if they can be shown to reproduce empirical data.

OBJECTIVES

Here, we evaluated the capability of one such mechanistic model to reproduce measured PCB concentrations in individual Norwegian women. We also assessed individual life-course concentrations.

METHODS

Concentrations of four PCB congeners in pregnant (n = 310, sampled in 2007-2009) and postmenopausal (n = 244, 2005) women were compared with person-specific predictions obtained using CoZMoMAN, an emission-based environmental fate and human food-chain bioaccumulation model. Person-specific predictions were also made using statistical regression models including dietary and lifestyle variables and concentrations.

RESULTS

CoZMoMAN accurately reproduced medians and ranges of measured concentrations in the two study groups. Furthermore, rank correlations between measurements and predictions from both CoZMoMAN and regression analyses were strong (Spearman's r > 0.67). Precision in quartile assignments from predictions was strong overall as evaluated by weighted Cohen's kappa (> 0.6). Simulations indicated large inter-individual differences in concentrations experienced in the past.

CONCLUSIONS

The mechanistic model reproduced all measurements of PCB concentrations within a factor of 10, and subject ranking and quartile assignments were overall largely consistent, although they were weak within each study group. Contamination histories for individuals predicted by CoZMoMAN revealed variation between study subjects, particularly in the timing of peak concentrations. Mechanistic models can provide individual PCB exposure metrics that could serve as valuable supplements to measurements.

Assessing the underlying breast cancer risk of Chinese females contributed by dietary intake of residual DDT from agricultural soils

The greatest concern over DDT exposure in China arose since the early 1990s for the rising breast cancer incidence, and the cause still remains to be elucidated. An extensive survey of DDT background in agricultural soils, covered the entire region of China, was conducted. DDT at concentrations greater than 100 ng/g (the China's Farmland Environmental Quality Evaluation Standards for Edible Agricultural Products) was found to impact 42.3 million Chinese population. Considering the geographical differences with diverse DDT contributions and different diet products and habits, the average daily dietary intake was modeled and estimated to be 0.34 μg/kg p,p'-DDE (the main bioactive constituent in DDT). Population attributable fraction derived from a case-control study from 78 women with breast cancer and 72 controls was used to assess the DDT exposure risk to breast cancer. Based on the estimated population attributable fraction with a median value of 0.6% (IQR 0.23-2.11%), the excess annual breast cancer incidence rate attributable to p,p'-DDE exposure averaged 0.06×10(-5) with significant spatial variations varying from 0.00021×10(-5) to 11.05×10(-5) in Chinese females. Exposure to DDT is a contributor to breast cancer, but the overall limited relative risk and population attributable fraction imply confounding factors for breast cancer in Chinese females. Exposure risk in a regional scale helps understand the cause and prevention of breast cancer. Our mapping and modeling method could be used to assess other environmental carcinogens and related cancer diseases.

Household and occupational exposure to pesticides and risk of breast cancer

The association between breast cancer in women and the use of household or occupational pesticides was examined in a population-based case-control study. This study was conducted in Western Australia in 2009-2011 and included 1,789 controls and 1,205 cases. Information on household pesticide exposure was collected from questionnaires. For occupational pesticide exposure, job-specific modules (JSMs) were used. To evaluate potential recall bias, we stratified the analysis by belief about whether pesticides contribute to breast cancer. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Women's exposures to pesticides in households and workplaces were not related to increased risk of breast cancer (OR = 1.10; CI: 0.86-1.37) and (OR = 0.77; CI: 0.45-1.32), respectively. The prevalence of occupational exposure to pesticides among women in our study was low. In the stratified analyses, the odd ratios associated with household pesticide use were similar among participants who believed pesticides increased breast cancer risk and those who did not. The results of our study did not show associations between breast cancer and household or occupational exposure to pesticides.