Learning Goals

In Submodule 1C you learned definitions of risk, safety, hazard and other common terms.

Terms such as "unsafe,"and "unreasonable risk" are subjective, and depend on who is evaluating the risk, and who is deciding how much risk is “acceptable.” Let us defer those questions of acceptable regarding risks to workers in the workplace to Module 4 next week and "safety" such as fire and explosion to Module 5 the week after. What we have left are general risks to human health and the environment due to waste being discharged - some type of waste being discharged somehow.

Assume we know of a waste problem and the exact chemical or chemicals being discharged. We would next need to know the amounts or concentrations to which humans and other receptors in the environment were exposed. From this and scientific evidence we would estimate the damage or risk of damage. Once all this was known, we could make a determination of the acceptability. For example, my neighbor's wood stove discharges 3 ppm of benzo-a-pyrene to my dog's environment, when the neighbor is burning wet wood and the wind is from the south. Knowing the weather predictions, a risk assessment expert determines the risk to my dog of lung cancer is one in ten million. I might then decide that risk is acceptable to me (I'm not sure if it is acceptable to my dog).

In the real world, it is often tough to determine the levels of chemicals at the sources, let alone at the receptors. The chemicals are subject to multiple variables that determine their fate and transport. The health and environmental effects are largely unknown. In the field of environmental risk assessment we do the best we can, and perhaps come up with a number, 1 excess death in 10,000 persons. Such numbers are our best effort, but we know they are just approximations at best; crude guesses at worst. Either way, is a calculated risk of 1 excess death in 10,000 acceptable? We might have an opinion, but most importantly, our (that's yours and mine) opinion of acceptability is of no real interest to anyone except you and me. (Now if the numbers you generate indicate a real threat that you are not comfortable with, you have an ethical obligation to do something about it. But often, the information the numbers are based upon is so vague, you don't feel confident enough to have a strong opinion.)

As a practical matter, we usually will determine both the risk and its acceptability by consulting a list that defines what is acceptable. When we find out that a chemical is on (or not on) a list, we are determining nothing scientific about the chemical, but we are determining its acceptability, to the agency that made up the list. It turns out there are many such lists, some generated by governments according to particular laws and regulations, others by standards-setting bodies. The lists may be specific regarding quantities or concentrations of chemicals that are unacceptable, or they may just name a chemical. (We'll talk about differentiating wastes and chemicals in Submodule 3B, for now let's just say chemical.)



Module 3 Index

ENVE 649 Homepage.