What Are Hazardous Substances?

Chemicals in our environment are a controversial subject. This is because their effects on human health are often not well understood. Both the government and the public want clear standards that define when a substance is considered “hazardous.” Unfortunately, it is not always easy to determine such a clear standard. Precise instruments allow us to detect a wide variety of substances even in very small concentrations. Sometimes these substances are only detectable in the parts per billion (ppb) or parts per trillion (ppt) ranges. In these cases, the concentrations are at or near the limit of our ability to even detect them.

If scientific study shows that a particular chemical is known or suspected to adversely affect our health, that substance could become listed as an official hazardous substance. The list of what “is” and “is not” a hazardous substance changes. With increased research, substances are added and, in some cases, removed.

The potential health implications make us question the presence of chemicals in our environment. It’s important to understand that any risk associated with a substance is dependent on both the concentration of the chemical and the length of exposure time. Some scientists believe that a “threshold” level exists for many chemical concentrations below which there are no known or anticipated adverse health effects. This allows standard concentration limits of some chemicals to be established. These standards are called “Maximum Contaminant Levels” (MCL), and they are enforceable by the Environmental Protection Agency. If these levels are exceeded, the substance must be cleaned up until it is at or below the MCL.

The term “hazardous substance” is used in this report as synonymous with “hazardous waste” and “toxic substance.” In general, the terms refer to a material with potentially harmful affects. Once a particular substance is determined to be harmful, it may become regulated by one or more environmental laws. When this happens, it is termed “listed.” Once a chemical is “listed,” sites that have spilled or leaked the substance may be required to clean it up.

Hazardous Substances in Perspective

As is true with any hazardous substance, the mere presence of it is not a threat to human health. In order to pose a health risk, that substance must come into physical contact with the body by eating, drinking, inhalation, or skin contact. It is the likelihood of physical exposure to a substance that must be carefully examined to determine an acceptable level of risk. Information on how contaminated sites can or cannot affect the property is vital in making decisions. Inaccurate perceptions could lead to making misinformed decisions. Two lines of logic to consider when analyzing risk are:

  • We make daily decisions based on familiar and acceptable levels of risk because we feel the benefits outweigh the potential consequences. For instance, although we know driving freeways might be dangerous, we drive them anyway because convenience and speed makes this risk acceptable. Many risks we undertake everyday aren’t considered hazardous simply because they are familiar.
  • Everyday, we make decisions based on what is most important to accomplish first, second, etc. This is necessary because if all problems were assigned equal importance, nothing could be accomplished. Risk is commonly considered similarly or, in other words, as “relative risk.” This consideration is based on deciding what “risk” has the worst or immediate adverse consequence and then address that risk first.

Often, decisions are not based on scientific analysis and hard data, but on perceived risk and public opinion. In the environmental arena, these two approaches go head to head. Public attention may be focused on certain environmental hazards based on a dramatic and well-publicized environmental problem. Unfortunately, this may lead to a diminished concern for other environmental issues that may pose more immediate concern. This line of thinking is not directed at undermining the significance of large-scale contamination, but is meant to direct attention to the “big picture.”

Many studies indicate that things we do on a daily basis in our homes may expose us to a greater overall health risk than living next door to virtually any contaminated site. It’s hard to imagine that many of the items we take for granted in our homes have higher concentrations of hazardous substances and expose us for greater amounts of time than just about anything we encounter in normal outdoor activities. This is where familiarity with items such as “drycleaned” clothes, many air fresheners, mothballs, paints or shoe polishes make the hazardous substances in such things acceptable. In certain cases, chemicals that are strictly regulated in industry are not regulated in homes. An example is methylene chloride, which the EPA found in about one-third of 1000 common household products in a 1987 study. Methylene chloride is regulated in factory emissions, but not within homes.

Understanding a variety of issues is important for making informed decisions. Evaluating risks accurately in order to avoid over— or under—reacting is a task best completed based on sound, accurate information.