COMMENTS BY RICHARD C. HERTZBERG, PH.D., ATLANTA, GA

Thankyou. A recent letterto the editor in ourAtlantaJournal Constitutic11 claimed that the EPA carbon rule and purported benefits are "based on flawed science". That is an easy claim to make, because nearly all science has some flaw, somefacet where we wish we knew more. Butthe writer's conclusions aboutthe application of the carbon rule and its benefits are absurdlywrong. Instead ofcountering those arguments, Iwant to add to EPA's statements ofwhywe need action now.

Iam a private consultant in biomathematics and an adjunct professor in Environmental Health at Emory Universitywhere Iteach environmental health risk assessment. One of myclassroom goals is to involve real environmental scenarios with real populations. In so doing, we address "cumulative risk," the risk from the 

### combinationof all the contaminants and stressorsthat we encounter at the same time. Why isthat importanttothe support ofthe carbon rule? In the latest U.S. National Climate Assessment report, it says: "Climate change is increasing the risks of heat stress, respiratory stress from poorair quality, and the spread ofwaterborne diseases." Elsewhere it states: "Heatwaves are also associated with increased hospital admissionsfor cardiovascular, kidney, and respiratory disorders." EPAAdministrator McCarthy, on EPA's website, says 

### 1 in 

### 10 children have asthma. In recent studies of some major cities, includingthe Oakland area and Detroit, they found about 

### 1 in 3 children were on asthma medication. One in Three.

EPA estimates how many asthma attacks and premature deaths woulclbe avoided by the required cuts in traditional air pollutants. Where EPAcould gofur• herwhen discussing the health benefits is to consider notjustthe separate risks, but the cumulative impactof all stressors together. My research specialty is toxic interactions, synergy and antagonism among chemicals. Of mostconc0m for public health is synergy, where the combination exposure is significantly more toxic than a
sum of individual exposures or risks would predict. So yes, we have**re~;ulations** on ozone, and on particulate matter (PMs), and on manyothercontamina1·ts in air. And
we worry about effects ofair pollution and heat waves on children. But our concerns should be much greater because ofthe combination effect ofthese stressors. Is there such evidence?

When evaluating health impacts of climate change, some studies estirn::_te the increase in ozone and its consequences on acute asthma attacks. Or h:w marry die from heatwaves. Or the impacts of particulate matteron several disease rates. Iam concerned that the EPA's estimates of health benefits from the carbon rule are similarly based on evaluations of each pollutant orcondition by itself. That can andshould be changed. Someveryfine epidemiology studies overthe past 

### 40 years here and in Europe looked atthe health consequences of air pollution in combination with heatwaves. Famous epidemiology studies over50years ago, such as those on cigarette smoke, "controlledfor" the otherfactors, so to identifythe contribution fmm the one pollutant of interest, such as cigarette smoke. Butthat single po lutant risk estimate does not represent a Real Exposure. In welcome contrast, these recent studies looked at the composite exposure conditions: real exposuresto ozone, PMs and heatwaves all together. Theyfound significantly increased risks from the combination for acute asthma and for early mortality. But the situation gets wmse. Another study on air pollution and asthma shows synergywith psychological stress from neighborhood violence. And where are many regions with high neifJhborhaod violence? Large cities. We thus have defined a highlyvulnerable populaion and one of considerable size.

The science of toxic interactions is complex, expensive, and difficultto quantify, one main reason why sofew regulations incorporate interactions. While we know rnJch about mechanismsfor high temperatures enhancing particulate mattertoxicity and for PMs enhancing ozone toxicity, we have not modeledthe 3-way interaction, nor the 4-waycombination that includes stress.

But these interaction effects have been documented and are already occurring to vulnerable populations, including children and the elderly. We see these exacerbated effects in asthmavisits at emergency rooms, and in increased mortality. These are not minor annoyances, but serious health conditions.

So should EPAdelay inclusion of interactions because we do not have 2. mathematical dose-response model? NO! As stated in EPA's own guidance for chemical mixtures risk assessment, even when only subjective information exists on the combination effects, thosejoint effects muststill be characterized tc the extent possible and reflected in the risk assessment.

In summary, EPA is doing preciselywhat is needed with this Carbon Ru.e, by acting NOW. Do not wait until all the desired mechanistic understanding and dose-response modeling have been accomplished. The interaction evidence is strong. rhe health impacts are here today, so we need action today.

Thankyou for your attention.