June 11, 2024

Potential impact on the cleanup standards for arsenic, EPA IRIS.On October 16, 2023, US EPA’s Integrated Risk Information System (IRIS) Program released an updated toxicological review for inorganic arsenic, which includes proposed changes to the toxicity factors. Many federal, state, and local agencies use IRIS toxicity factors to assess environmental risk and establish risk-based environmental standards.

For example, the State of Florida and Miami-Dade County derived their direct exposure Soil Cleanup Target Levels (SCTLs) using these toxicity values, per Chapter 62-777, Florida Administrative Code and Chapter 24-44(2), Code of Miami-Dade County. If adopted, the updated toxicity values will lead to lower arsenic cleanup standards and, as a result, will significantly impact the assessment and remediation of contaminated sites throughout Florida.

Toxicity Factors Under Review and Potential Impact

The specific toxicity factors under review are the oral cancer slope factor (CSFo) and the oral reference dose (RfDo). In the current draft of the updated assessment, the IRIS Program has proposed a CSFo of 53 mg/kg/day for combined cancer risk and an overall RfDo of 0.031 µg/kg/day to protect against all noncancer adverse health effects associated with inorganic arsenic across all life stages.

To illustrate the significance of these updates, we used the proposed CSFo to re-calculate the State of Florida SCTLs. The resulting SCTLs would decrease from the current Residential SCTL of 2.1 mg/kg to 0.1 mg/kg and from the current Commercial/Industrial SCTL of 12 mg/kg to 0.4 mg/kg (assuming all other exposure factors remain the same). If the proposed changes to the toxicity factors are approved, remediation in Florida could feel the impact. An environmental engineer/consultant knowledgeable in due diligence, background assessments, and risk assessment/management can help you navigate these changing regulatory requirements.

toxicological review for inorganic arsenic

Rulemaking Process At Midpoint

The following links will direct you to the proposed toxicological review, a summary of the comments received during the public comment/peer review process, and information on the general assessment review process:


Given the potential impact on the cleanup standards, it is important to remain current with this updated assessment’s development and keep our clients informed of the potential changes. EPA is reviewing over a hundred comments received on the October 2023 draft IRIS Toxicological Review of Inorganic Arsenic. We understand that the final document’s projected release date will be announced once the Science Advisory Board delivers its peer-reviewed report. We’ll keep you informed.


Additional Resources:

 About Arsenic

Arsenic is a naturally occurring trace element in the environment. It is in geological formations, and levels in soil can range from 1–40 milligrams per kilogram (mg/kg). Erosion, leaching, and some human activities can increase arsenic levels in soil. Arsenical pesticides were once commonly used in agriculture to maintain turf (e.g., golf courses, parks, etc.) and treat wood. While their use has been significantly restricted, residual concentrations can still be detected during an environmental site audit/assessment.

Land Remediation and Brownfields: Information, case studies, grants, and educational materials.


Anabel Rodriguez Garcia

Meet our Authors: Environmental Scientist Anabel Rodriguez Garcia and Lisa Smith, a principal technical advisor and expert in risk-based corrective action.





Posted by Diane Samuels at 6:00 am