Safe harbor levels; a closer look

Prop-65 was enacted with two bold parts to it. The first, ‘Safe Drinking Water,’ prohibited companies from discharging any of over 900 regulated chemicals into or near a water source, thereby protecting the groundwater. The second, the ‘Toxic Enforcement Act,’ required companies to put a warning label on their product if it contained one or more of the regulated chemicals in amounts above:


Let's take a closer look at these regulations.

Chemicals—especially food additives or elements—undergo extensive studies to determine their safety. In most cases, these studies are done on animals (typically rodents) who are given varying dosage levels of a chemical over a period of a few months to a few years. From these studies, a qualified pharmacologist, toxicologist, or group, may determine a no-observed-effect-level, or NOEL, which establishes the amount of a chemical that is shown to cause no biological harm. In cases where a NOEL has not or cannot be established, the lowest-observed-effect-level (LOEL) may be divided by a conservative safety factor of ten and used as the NOEL instead.

For chemicals linked to reproductive harm or birth defects, Prop-65 law takes the NOEL and divides it by 1,000 to "provide an ample margin of safety." This becomes their Maximum Allowable Dose Level, or MADL. Any food, product, or service that might expose a consumer to an amount above this level must carry the Prop 65 warning for reproductive toxins.

Let's see how this process worked with cadmium in 2001.

First, the Office of Environmental Health Hazard Assessment (OEHHA) reviewed available studies on cadmium toxicity to choose the most relevant, sensitive, and thorough. Two studies were selected that met their criteria, and of the two, the one that had the lower dosage levels associated with a health outcome was selected as the benchmark for Prop 65 safe harbor calculations.

This study had a LOEL, but not a NOEL. To get from one to the other, the average daily cadmium intake for the LOEL group, 0.706mg/kg/day, was divided by 10 to get a NOEL of 0.0706mg/kg/day. When this number was multiplied by the average weight for a pregnant woman (58kg) the result was:

0.07mg/kg/day x 58kg =- 4.1mg/day

Put another way, 4.1 milligrams was established as the amount of cadmium that could be consumed daily by adults, including pregant or breastfeeding women, that would have no effect on reproductive health.

From here to the Prop-65 MADLs, this number was divided by one thousand to get:

4.1mg ÷ 1,000 = 4.1mcg/day

Thus, 4.1 micrograms (0.0041mg) and above was established as the amount of cadmium that fell under Prop 65's right-to-know labeling laws.

Whew! Still with us? If you are, great! Let's move on to the cancer warning.

OEHHA detrmines cancer risk by a slightly more complex process. The beginnings are similar; collecting the studies, examining the methods, analyzing the results, and determining which studies are the most relevant and accurate. From here, some serious math is used, like this one, called the Mathmatical Model for Carcinogenesis:

p(d) = 1 - exp[-(q0 + q1d + q2d2+ ... + qjdj)]

While we won't pretend to understand these equations, we can appreciate the final outcome, called the No Significant Risk Level (NSRL) for cancer. Prop 65 defines this level as "not more than one excess case of cancer in 100,000 individuals exposed to the chemical over a 70 year lifetime."

Let's explore this more, using lead as our example.

An analysis of rodent studies in 2002 by the OEHHA resulted in a NSRL of 15mcg/day. In other words, at an intake of 15mc/day, no more than 1 individual out of 100,000 would be at risk of developing cancer over an assumed 70 year lifetime. Any food, product, or service that might expose a consumer to an amount of lead above this level must carry the Prop 65 warning for cancer. (Note that lead has a MADL established at 0.5mcg and will carry the reproductive toxins warning for amounts at or above this level.)

What about chemicals without NOELs, LOELs, MADLs, or NSRLs?

Roughly 600 of the more than 900 chemicals that fall under Prop 65 labeling laws currently have no established Safe Harbor levels. This means that all products or service containing them in any amount must carry a Prop 65 warning label. 

Where does this leave you, the consumer? Well, it's important to first remember that Prop 65 is a right-to-know law, and not a determinant of safety. In assessing the risk that a product might pose to you, as an individual, you should consider your current health state, assess the source and amount of chemical exposure, and—if you have any lingering questions or concerns—reach out to your health professional for guidance.

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