Why Isn’t Risk Assessment Done on All Chemicals?

I have recently been asked why are there so few occupational exposure limits compared to the number of chemicals in commerce?   There are a number of potential answers to this but I think the simplest and most accurate comeback is that there is a lack of data.   So that begs the question as to why there is so little data?

We all probably know by now that Human Health Risk Assessment is the integration of the ability of a chemical to cause harm to human health with the actual exposure to that chemical that might occur in the real world.   In terms of a simple conceptual model:   Risk = (Toxicological Harm/Exposure)X(Exposure).    EVERY chemical will cause toxicological harm at some dose.   Pure oxygen breathed for an extended period is toxic.  Indeed Wikipedia reports that pulmonary and ocular toxicity result from extended exposures to elevated oxygen levels at normal pressure.   Given a dose high enough, toxicological harm comes from each and EVERY chemical we can think of.  The “what” of that untoward health outcome is called the HAZARD IDENTIFICATION for that substance. In the above example with oxygen it is pulmonary and ocular toxicity.  It is usually the first bad thing health-wise that happens as you ramp up the exposure level and it can range from irritation to more serious outcomes like cancer to death.   The exposure level over which that bad health effect happens defines the POTENCY of the chemical’s toxicological effect with highly potent materials causing effects at very low exposures.   Oxygen is not very potent.  By comparison benzene is very potent in its ability to cause toxicological harm.

The point of all this is that you cannot begin to do a risk assessment without data on the toxicological properties (HAZARD IDENTIFICATION and POTENCY) of the chemical of interest.  If you have No data you have No risk assessment unless you really force the issue which will be discussed below.

Unfortunately, what has sparked a lot of the toxicological data that we have comes from first seeing the adverse health effect of the chemicals on exposed humans.   Benzene falls into this category.   So does asbestos and vinyl chloride and all the other known human carcinogens.   Seeing people stricken by these substances caused them to be studied.   The other category of well-studied chemicals is pesticides.  This is primarily because they are designed to be commercial poisons so they are expected to be relatively potent toxicants and clearly worthy of study.   As a result they are also highly regulated.  How do we address the rest of the chemicals in our world?

In the late 1990s the Environmental Defense Fund issued a ground breaking report entitled:  Toxic Ignorance (The Continuing Absence of Basic Health Testing for Top-Selling Chemicals in the United States):  http://www.edf.org/sites/default/files/243_toxicignorance_0.pdf    It proved with undeniable hard data that, at that point in time, “…even the most basic toxicity testing results cannot be found in the public record for nearly 75% of the top volume chemicals in commercial use.”   As you might imagine it caused quite a stir and the EPA got involved and eventually hatched the High Production Volume (HPV) Challenge  program.  http://www.epa.gov/hpv/.   This resulted in considerably more toxicological data but as you might guess there remains a severe lack of data for the tens of thousands of chemicals still in commerce to which folks are exposed every day.

But that takes us to an even more fundamental question:  Why haven’t we been testing the chemicals that we breathe, eat and touch in our environment to determine their toxicological effects all along?   Why has it taken the cold hand of public scrutiny and regulation to get things moving?  I think one of  the strongest factors addressing this question is the misguided presumption of safety by those with an economic stake in these chemicals.   Many believe at some level that “no proof of risk means proof of no risk.”  This is, of course, not true; however, for these folks there is no incentive to go “looking for trouble” by testing the chemicals to identify the hazard they pose and the potency of that hazard.   Toxicology testing is, or has been, considered to be relatively expensive to do so.   Thus, the reasoning goes, why spend money to give you bad news when you assume it’s safe and the testing would only bring bad news?

There is another large factor in this and that is the mistrust of toxicological data.   Those who do not like the results point to the high doses used in the toxicological studies and assert that they do not relate to or represent the exposures received in the real world and are therefore unrealistic measures of risk.   We will get into these issues (dose-response extrapolation and setting exposure limits) in future blogs but I think you can see how the politics might be playing out in all this to have a strong bias towards not doing toxicological testing.

So at the end of 2013 we are left with lots and lots of chemicals but relatively little toxicology data to characterize the hazard and potency of these tens of thousands of substances in commerce.   My sense, however, is that as Bob Dylan once sang “The times they are a changin…”   The European REACh statute is essentially driving risk assessment by forcing risk assessment and the assignment of exposure limits based on very prescriptive procedures.  I will go over REACh in a future blog because I believe it has the capacity, given the political will, to ultimately drive the science of risk assessment.   This could conceivably force much more testing of both toxicity and exposure but that remains to be seen.
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On another front the EPA is spending considerable money (tens and perhaps hundreds of millions of USD) and resources in advanced toxicological screening using innovative molecular biology techniques in a program entitled ToxCast:  http://www.epa.gov/ncct/toxcast/     

More confident data will begin to feed the risk assessment process which should ultimately the lower uncertainty of the analyses.  Lower uncertainty will, in turn, lower the forced overestimation of risk that comes from doing a risk assessment with a lack of data.  Indeed, in the end this confident knowledge will be much more cost-effective in focusing on real risk and not spending money on phantom risk borne of uncertainty.