Environmental lab report distribution, May 2002

NYC 9/11 Public Portal Document

In cases where appropriate standards did not exist, risk-based criteria were developed using EPA risk assessment methods: for indoor air, methods described in EPA’s “Hazard Evaluation Handbook: A Guide to Removal Actions” were used; for dust, EPA’s “Wipe Sample Assessment” guidance was used. The risk-based criteria reflect the most current toxicity criteria (slope factors and RfCs) on EPA’s IRIS database.

Individual sampling results that exceed benchmark values should not be interpreted to represent the occurrence of an adverse health effect. Rather, such information indicates the need for careful monitoring and the assessment of longer-term data trends for evaluation against appropriate health criteria. That is, most of the screening levels have been developed to account for continuous one-year average exposure durations. Because these screening levels assume continuous exposure for an extended duration, the average of the measured concentrations is more appropriate for evaluating risk than an individual measurements. Consequently, miscellaneous individual values above the screening level may not necessarily be indicative of potential for concern.

Developing Risk-Based Criteria for Indoor Air

For carcinogenic compounds, the benchmarks were set so that a local resident’s lifetime risk of developing cancer from exposure to WTC-related contaminants for a certain amount oftime would be only one-in-ten-thousand greater than the resident’s normal risk without this exposure (in risk assessment terms, the excess lifetime cancer risk was set at E-04). The amount of time that residents and office workers were exposed to WTC-related contaminants is unknown. To be conservative, the Tier I action level was chosen to be protective of a resident who may have been exposed to WTC-related contaminants for one year. The Tier HI no-action-needed level was chosen to be protective of a resident who is exposed to WTC-related contaminants for 30 years (which is the upper-bound estimate for residency in one dwelling). The 30-year and 1-year exposure durations reflect an apportionment between child (20% of total exposure duration) and adult (80% of total exposure duration) receptors. Because children have comparatively greater (as a function of body weight) respiration rates than adults, the benchmark levels developed are marginally more stringent than values that would otherwise be derived by direct application of IRIS-verified Unit Risk values.

For non-carcinogenic compounds, a resident’s daily intake of a contaminant is compared to the Reference Dose, which is the amount of a noncarcinogenic compound that someone may take in per day without adverse health effects. That comparison is called the Hazard Quotient (chronic daily intake/Reference Dose). According to EPA guidelines, if the Hazard Quotient is greater than one, there may be concern for potential health effects. Therefore, for Tier III, the no-action-needed level, the benchmark was chosen for a Hazard Quotient (HQ) of 1. For Tier I, the action level, a Hazard Quotient of 10 is used, in accordance with the Hazard Evaluation Handbook. An HQ of 10 is used to account for the fact that chronic toxicity criteria (RfDs/RfCs) are being applied to sub-chronic exposure scenarios that are not expected to exceed 6 months - 1 year in duration. Accordingly, a Hazard Quotient of 10 was used for non-carcinogens to reflect a similar (i.e., upper bound of 1 year) exposure duration. Note that contaminants (both non-carcinogens and carcinogens, alike) can exhibit acute effects from short-term, high-dose exposures. Because the benchmark levels are based on subchronic

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