Toxic Tuesdays
CHEJ highlights several toxic chemicals and the communities fighting to keep their citizens safe from harm.
Cumulative Risk and Toxicity
Evaluating the cumulative impacts of exposure to multiple chemicals is perhaps the most difficult task facing toxicologists. The standard approach is to evaluate these risks by conducting a risk assessment or risk evaluation which relies heavily on data from exposure to a single chemical. But this only provides a limited assessment of the risks. Over the years there has been a growing recognition that this approach has many flaws (see previous issues of Toxic Tuesday) and limited application to real world exposures to multiple chemicals at low concentrations. EPA has recognized the need to develop tools to evaluate cumulative risks, but has failed to develop a clear road map for how to do this.
A cumulative risk assessment would analyze the combined risks to health or the environment from exposure to multiple agents or stressors (USEPA 2003). This process includes evaluating the risks posed by exposure to multiple toxic chemicals simultaneously and over time as well as the influence on health of stressors such as genetics, lifestyle choices, income and air quality.
Evaluating cumulative risks requires knowledge of what chemicals a person was exposed to, the concentration of each of the substances in the mixture and how long a person was exposed to each of these substances. It also requires knowledge of how these chemicals in combination react to each other and how these chemical interactions in mixtures potentially impact human health. It also necessitates knowledge about the health status of each person exposed. There is both a natural variability as well as unique susceptibility among a group of people that influences health outcomes. For example, people who are sick or who have existing health conditions such as a weak heart or compromised immune system can influence how a person responds to a mixture of chemicals. Socioeconomic factors such as poverty, unemployment rates, education levels and income also influences how people in a community respond. All of these factors combined would have to be considered to assess the cumulative health impact resulting from exposure to multiple chemicals simultaneously.
What’s become very clear over the years is that the scientific community knows very little about most of these factors. Consequently, risk assessors need to make many assumptions about information that is not known or at best uncertain. This is especially true when it comes to information about exposures (concentration and for how long) as well what level of exposure actually triggers harm in the body. The lack of knowledge and understanding of the molecular interactions have made it very difficult for scientists to forecast what will happen when people are exposed to multiple chemicals at low concentrations over time and why the field of toxicology has struggled to address multiple chemical exposures.
This failure has left community leaders and people in communities exposed to multiple chemicals simultaneously frustrated by the lack of answers and the lack for action by government agencies when addressing multiple chemical exposures. It may also be frustrating for government agencies because they are dependent on a tool (risk assessment) that relies on an antiquated approach that cannot answer the questions that people are asking.
EPA and other public health agencies need to be honest and truthful with the public about what they don’t know about chemical exposure risks. Scientists actually don’t know very much about what happens to people exposed to low level mixtures of toxic chemicals. While this reality may not be reassuring, the truth allows everyone to better understand what they are facing.
There is an alternative that should be considered. EPA should follow the lead of what the government did to take care of Vietnam Veterans who were exposed to Agent Orange and the soldiers exposed to emissions from the burn pits in Iraq and Afghanistan, among others. In these cases, soldiers do not have to prove that their illnesses were caused by their exposure to toxic chemicals. If they can show that they were exposed and that they have an illness associated with the chemicals they were exposed to, that’s sufficient for them to get health care and other compensation.
Communities exposed to toxic chemical mixtures shouldn’t be held to a different standard given that the uncertainties about toxic exposures are driven by the same scientific unknowns. In the absence of a basic understanding of what adverse health effects might result from exposures to the mixtures of toxic chemicals released into a community, the government should take steps to address the needs of the community, whether it’s by providing health care for those who were exposed or establishing a medical monitoring program to follow these people, or both.
These steps will begin the long and difficult process of acknowledging what we know and don’t know about exposes to low level mixtures of toxic chemicals and begin to learn what happens to the people exposed in these situations.
Previous issues of Toxic Tuesday
Learn about more toxics
Cumulative Risks and Toxicity
Evaluating the cumulative impacts of exposure to multiple chemicals is perhaps the most difficult task
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