New Mexico Health and Environment Linkage Studies describe linkage study goals, methods, data sets, metadata, findings, and recommendations for reducing risk. The paragraphs below discuss some of the issues and limitations involved with associating environmental data to health data. The NM EPHT Program has explored specific health and environment linkages for Asthma and Ozone and Cancer and Arsenic in Drinking Water.

NM Linkage Study Report: Asthma and Ozone in San Juan County (PDF)

NM Linkage Study Report: Drinking Water Arsenic and Bladder Cancer by County (PDF)

Linkage studies refer to investigations that connect environmental and health outcome tracking data in time and place within a population. The primary goal of linkage studies is to facilitate understanding of the relationship between diseases and the environment, and where possible, help inform public policy decision making. A good example of the impact such studies may have is the removal of lead from gasoline in the 1970’s following a series of national linkage studies showing that blood lead levels decreased in direct relation to declining lead use in gasoline. In this instance, a clear cause-effect relationship existed between environmental hazard and health effect, and measuring the declining lead content of gasoline was relatively easy to do. Unfortunately, for many diseases the cause-effect relationship is not clear, and environmental hazards cannot be measured as easily. Furthermore, many adverse health outcomes may result from exposures to multiple different hazards, some received in the short term and others received over a longer, more protracted time period. For these reasons, it is important that linkage be approached in a scientifically rigorous manner. However, even here, caution is needed in the interpretation of results since the environmental data used in linkage analysis ordinarily is not collected on an individual basis, but rather, across broad populations, such as a county or particular region within a state. Consequently, a study that does find a relationship between the level of an environmental hazard and the occurrence of a health outcome cannot be used to conclude that the hazard actually caused the health outcome since it is not known who among the population actually received exposure at the levels of interest. Rather, the results of such studies can be used to generate hypotheses on causation, which can then be tested in more formal studies involving recruitment of study subjects and collection of data on an individual level.

The approach to linkage in New Mexico has been to identify environmental hazards of local concern and then explore how variation in hazard levels may be related to variation in the occurrence of relevant health outcomes. One particular area of interest has been arsenic in drinking water. Beginning in 2006, all public water supply systems in the U.S. were required to provide drinking water containing no more than 10 ug/l of arsenic. Prior to this date, the standard for arsenic had been 50 ug/l, and was revised downward by the U.S. Environmental Protection Agency (EPA) in 2001 due to concerns that the standard was not sufficiently protective of public health. Arsenic in drinking water at relatively high levels has been causally associated with a variety of adverse health outcomes, including certain forms of cancer, particularly lung and bladder, kidney disease, cerebrovascular disease, and diseases of the heart. Considerable scientific debate accompanied the EPA decision to lower the arsenic standard, including concerns that the 10 ug/l level was still not sufficiently protective of public health. Although many areas of the country are supplied with drinking water containing no more than trace amounts of arsenic, in New Mexico the situation is different in that a significant portion of the state population historically has been provided drinking water containing between 10 ug/l and 50 ug/l of arsenic. In light of the uncertainty in the nature of health risks from low– to moderate–level arsenic, linkage studies have been initiated in New Mexico to investigate whether the variation in drinking water arsenic levels across the state is related to certain adverse health outcomes. Bladder cancer is of particular interest, since this form of cancer has been most strongly associated with drinking water arsenic. Using environmental and health data from the state EPHT program, linkage studies underway in New Mexico are seeking to determine if the incidence of bladder cancer is higher in those parts of the state where higher drinking water arsenic levels exist. In addition, based on recent research suggesting that arsenic exposure may lead to more aggressive forms of bladder cancer, the studies are also seeking to explore trends in clinical presentation of bladder cancer at diagnosis in relation to drinking water arsenic.

NM Linkage Study Report: Asthma and Ozone in San Juan County (PDF)

NM Linkage Study Report: Drinking Water Arsenic and Bladder Cancer by County (PDF)