Cancer Risk & Environ. Exposures to Nitrate,Pesticides,

研究环境中农业暴露的癌症危险因素，以估计这些环境暴露对农村人口癌症的贡献。农村人口在饮用水中接触杀虫剂和硝酸盐的程度介于职业接触群体和一般人群之间。对非霍奇金淋巴瘤和脑癌、膀胱癌、结肠癌、直肠癌、胃癌、食道癌、胰腺癌和肾癌进行了病例对照研究。在这些病例对照研究中，为例行监测目的收集的水污染物数据库被用来估计过去通过公共供水对个人的接触。爱荷华州公共供水中的硝酸盐水平与膀胱癌和胰腺癌的风险无关。然而，较高的饮食亚硝酸盐摄入量与胰腺癌的风险增加有关。总的来说，饮用水中的硝酸盐含量与结肠癌的风险无关；然而，亚硝化能力增加的特定亚组风险增加。内布拉斯加州公共饮用水中硝酸盐含量升高与非霍奇金淋巴瘤风险增加有关。对暴露水平较低的明尼苏达州饮用水中硝酸盐的分析发现没有关联。内布拉斯加州公共供水中硝酸盐含量升高与女性患神经胶质瘤的风险增加有关，而与男性无关。最近在爱荷华州、西雅图和底特律地区完成的一项非霍奇金淋巴瘤病例对照调查正在进一步研究这一假设。在对内布拉斯加州和科罗拉多州普拉特河谷的人口普查群体进行的生态学研究中，硝酸盐作为癌症风险因素的问题正在得到进一步的探讨，那里的硝酸盐水平是全国最高的。利用土地覆盖、牲畜饲养场位置、土壤类型和其他信息来估计私人水井中的硝酸盐水平。我们还在开发新的方法，并改进现有的方法，在一般环境暴露研究中进行暴露评估，重点是农药和硝酸盐。这是为了更好地估计风险，并发现在此类研究中经常遇到的相对较小的风险增加。目前正在利用地理信息系统开发新的方法来估计农药的间接接触和估计私人水井中硝酸盐的接触。利用遥感数据（卫星图像）和历史记录来估计内布拉斯加州和爱荷华州的人口，因为他们的家靠近农药处理过的农田，可能暴露于农业农药。与州农药使用报告数据库一起，这种方法也被用于改进加利福尼亚州的农药接触评估。在爱荷华州和加利福尼亚州正在进行验证研究，以确定家中的农药水平与已施用农药的农业用地的邻近程度之间的关系。

Risk factors for cancer from agricultural exposures in the ambient environment are studied to estimate the contribution of these environmental exposures to cancer in the rural population. Rural populations have exposures to pesticides and nitrates in drinking water that are intermediate between occupationally-exposed groups and the general population. Case-control studies have been conducted on non-Hodgkin's lymphoma and cancers of the brain, bladder, colon, rectum, stomach, esophagus, pancreas, and kidney. Databases of water contaminants, gathered for routine monitoring purposes, are being used to estimate past exposures via public water supplies to individuals in these case-control studies. Nitrate levels in public water supplies in Iowa were not associated with risk of bladder and pancreas cancer. However, higher intakes of dietary nitrite were associated with an increased risk of pancreas cancer. Overall, drinking water nitrate levels were not associated with risk of colon cancer; however, specific subgroups with increased nitrosation ability were at increased risk. Elevated nitrate levels in public drinking water supplies were associated with an increased risk of non-Hodgkin's lymphoma in Nebraska. An analysis of nitrate in drinking water in Minnesota where exposure levels were lower found no association. Elevated nitrate in public water supplies in Nebraska was associated with an increased risk of glioma in women but not men. This hypothesis is being investigated further in a recently completed case-control investigation of non-Hodgkin's lymphoma in Iowa, Seattle, and the Detroit area. The issue of nitrate as a cancer risk factor is being pursued further in an ecologic study of census-block groups in the Platte River Valley of Nebraska and Colorado, where elevated nitrate levels are among the highest in the country. Nitrate levels in private wells are being estimated using data on land cover, livestock feedlot locations, soil type, and other information. We are also developing new approaches, and improving existing methods, of exposure assessment in studies of general environmental exposures, with a focus on pesticides and nitrate. These are required to better estimate risk and to detect the relatively small increases in risk often encountered in such studies. Geographic information systems (GIS) are being utilized for developing new approaches to estimating indirect exposure to pesticides and for estimating exposure to nitrate in private wells. Remote sensing data (satellite imagery) and historical records were used to estimate the population in Nebraska and Iowa potentially exposed to agricultural pesticides through the proximity of their homes to agricultural land treated with pesticides. This approach is also being used to improve pesticide exposure assessment in California in conjunction with the State pesticide use reporting database. Validation studies are underway in Iowa and California to determine the relationship between pesticide levels in the home and the proximity to agricultural land where pesticides have been applied. Pesticides A feasibility study using remote sensing data and a GIS to estimate indirect exposure to pesticides demonstrated that using available data, accurate historical crop maps could be produced and that these could be linked to pesticide use data to estimate probabilities of indirect exposure to agricultural pesticides. A total of 24% of the study population in an agricultural area were determined to live within 500 meters of crop fields likely to have been treated with pesticides. This was the first study to estimate the prevalence of potential indirect exposure to agricultural pesticides in the general population. Further work in this area by our collaborators included the development of a method to automate crop mapping from satellite imagery. The method was found to be successful at classifying crops into two categories: corn and other crop types, over a 15 county area of Nebraska. We are continuing to refine the GIS-based approach to estimating agricultural pesticide exposure by incorporating information from a pesticide drift model. A validation study is underway in Iowa to compare agricultural pesticide levels in carpet dust samples with several GIS-based exposure metrics including one that incorporates information on wind direction and pesticide drift. With collaborators in California, we are planning to evaluate agricultural pesticide use near residences as a risk factor for childhood leukemia in an ongoing study. Carpet dust samples will be analyzed for pesticides, and information about the current and historical location of crops near residences will be determined. Using a GIS, residential proximity to specific industries, hazardous waste sites, and specific chemical releases as reported by the Environmental Protection Agency's Toxic Release Inventory will be evaluated in an ongoing case control study of bladder cancer in New England. The first steps have been to evaluate the feasibility of geocoding past residential histories from a pilot study in New Hampshire and to determine the historical locations of specific industries associated with bladder cancer risk.