Exposures to Chemical Mixtures

Since Friedrich Wohler first synthesized urea in 1828, it is estimated that more than 1 million chemicals that were previously unknown in our environment have been synthesized. There are more than 80,000 chemicals mannfactured and imported into the United States each year. People are exposed to most of these by air pollution, water pollution, foods and food chain transfers, soil contamination, household use of chemical products, the use of personal care and pharmaceutical products, and industrial contact. Exposure begins before birth in utero and continues throughout life. The different modes of exposure will be dealt with separately in the following chapters. 

TRI is the most detailed source of information about toxic chemical releases. TRI, however, seriously underreports the total toxic chemical releases for the following 

TRI does not cover all industries. Prior to 1998, for example, metal mining and electric utilities were not required to report their toxic chemical releases. 

TRI reports on less than 1% of the 80,000 chemicals annually manufactured and imported into the United States. It covers only about 650 of the chemicals in use in the United 

Reporting companies estimate their emissions by using emission factors rather than by actually monitoring their emissions. 

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Current knowledge about the combined toxicological effects that may occur from exposures to different chemicals in mixtures is outlined in this chapter. Special attention is paid to the low levels of exposures normally encountered from the unintended, indirect exposure to chemical mixtures through food and environment. It should be recognized that it has not been possible to cover all possible combined exposures to chemicals in this book. 

US-EPA. 1986. Guidance for health risk from exposure to chemical mixtures. U.S. Environmental Protection Agency, Fed Reg 51 34014. 

In order to evaluate an individual s exposure to chemical mixtures, it was necessary to determine how frequently pesticide and industrial chemicals were found in each food product. The results of this determination are discussed for the basic food categories (i.e., dairy, protein, vegetable, fruit, and grain) as well as for the mixed food and child/infant food categories. 

The previous discussion has focused on an individual s exposure to synthetic chemicals in a balanced diet, yet many individuals choose to eat only specific foods that fit their lifestyle preferences. Thus, it is important to look at how specific diets can affect an individual s exposure to chemical mixtures. 

Interactions Affecting Availability and Exposure to Chemical Mixtures.10... 

As described, living organisms are constantly exposed to vast amounts of chemicals, that is, to 1 big chemical mixture. We lack the information on how to properly capture the entire exposure, on how to address the toxicity, and how to evaluate the associated risk. Therefore, the initial approach is to properly define mixtures on a smaller scale. These are the mixtures of concern and are usually associated with a specific exposure scenario and possible health implications. Exposures to chemical mixtures of concern can range from simple and well-defined mixtures to complex and poorly defined mixtures. For example, morphine in combination with other epidural anesthetics is used in hospital settings for pain relief. The mixture can be characterized as simple (<10 chemicals), and in some cases such mixtures can be well defined because it is easier to identify the chemicals involved and know their dose, toxicity, and potential interactions. In contrast, complex mixtures are composed of many (>10) chemicals. Their composition may be largely known or at least reproducible (e.g.,... 

INTERACTIONS AFFECTING AVAILABILITY AND EXPOSURE TO CHEMICAL MIXTURES... 

Hearl FJ. 2005. Occupational exposure to chemical mixtures. Presented at the First International Conference on Environmental Exposure and Health, Atlanta (GA). 

What do Gulf War Syndrome, Katrina Cough, Aerospace Syndrome, and epidemic increases in the incidence of autism, Attention Deficit Hyperactivity Disorder (ADHD), birth defects, asthma, mailroom illness, spontaneous abortion, and many cancers have in common Each of these can be associated with a single causative agent, but each can also be associated with environmental exposure to chemical mixtures that do not contain any of the known causative agents. 

Our inability to defend ourselves against new chemicals and mixtures often results in epidemics of disease. For example, asthma, autism, infertility, and many cancers affect different parts of the body and seemingly have different etiologies. All, however, can be related to a combination of genetic predisposition and environmental exposure to chemicals. All are less prevalent where chemical exposures are lower, for example, in rural areas. All have known single chemical exposure causes and they can all be related to low level exposure to chemical mixtures. The toxic effects of chemical mixtures are explored in the chapters that follow. 

As noted in the introduction, exposure to chemical mixtures can produce enhanced effects, low level reactions, and unpredicted points of attack. The toxicological literature has reported these but until recently was at a loss to offer an explanation. The following published studies are illustrative of how toxicologists viewed the unexpected effects of exposures to mixtures prior to 2003. 

The majority of xenobiotics that are absorbed by the body are lipophilic and can permeate through body membranes. The uptake of hydrophilic species by the body, however, be they solvents, pharmaceuticals, or other chemicals are facilitated by the presence of lipophilic species. Kow values predict which chemicals are hydrophiles and which are lipophiles. Exposures to chemical mixtures of lipophiles and hydrophiles will result in the absorption of greater quantities of hydrophiles than would be taken up if these species were present alone. 

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