Is PBO an Endocrine Disruptor? What Endocrine Studies have been Conducted on PBO?

The Food Quality Protection Act (FQPA) of 1996 required the U.S. EPA to address the issue of endocrine disruption.  Since the passage of the FQPA, U.S. EPA has developed a two-tiered Endocrine Disruptor Screening Program (EDSP) designed to examine potential effects of substances on the Estrogenic, Androgenic and Thyroid (EAT) hormone systems in both humans and wildlife.  Tier 1 consists of 11 assays, and is designed to determine whether a substance has the potential to interact with the (EAT) hormone systems.  If results indicate a relationship, the chemical progresses to Tier 2 testing.  The purpose of Tier 2 is to determine whether a substance that interacts with the EAT hormone system exerts an adverse effect in humans or wildlife, and to develop a dose-response that, in association with exposure data, can be used to assess risk.

PBO is one of the chemicals selected by U.S. EPA to be part of the initial effort under the EDSP.  U.S. EPA’s issued its first list of chemicals for EDSP testing in 2009, consisting of over 60 pesticide chemicals, including the insecticide synergist PBO.  It is important to note that the first list of chemicals for EDSP screening is not based on a potential for endocrine activity or a potential for adverse effects.  Rather, the list is based on an U.S. EPA prioritization regarding exposure potential. PBO was added to this list because of its wide use pattern (1500 products registered with U.S. EPA), people may be exposed to low levels of PBO in the diet, from treated surfaces in the home (e.g., carpet), and in certain occupations (e.g., pest control operator).

What do the data tell us about PBO and Endocrine disruption?

No evidence suggests that PBO disrupts the normal functioning of the endocrine system.  This includes the recently developed data to assess the possible interaction of PBO with the endocrine system.  The PBTFII has conducted all 11 EDSP Tier 1 screens and has submitted all required documentation and study reports.

How will these studies be evaluated?

U.S. EPA intends to use a Weight of Evidence (WoE) approach for assessing EDSP Tier 1 results.  While the Agency issued WOE Guidelines (EPA 2012) no actual WOE assessments have yet been conducted and released to the registrants.  The PBTFII has conducted a WoE analysis for PBO that is consistent with U.S. EPA’s Guidelines.  The WoE analysis for PBO examines each EDSP Tier 1 assay conducted for PBO.  It discusses the purpose of the assay, and summarizes the study design and results and provides an overall conclusion for each assay.  All 11 individual assays are then considered together to arrive at an overall conclusion for the outcome of the Tier 1 battery.  For some assays, Other Scientifically Relevant Information (OSRI) is also considered as part of the assessment.

The purpose of this WoE analysis is to determine whether PBO has the potential to interact with the endocrine system, as determined by EDSP Tier 1 assays, the Tier 1 battery as a whole and OSRI.  A determination that a chemical has the potential to interact with the endocrine system would trigger a need for EDSP Tier 2 testing.

Based on a careful analysis of the Weight of Evidence with respect to PBO, the PBTII concludes that PBO does not interact with the Estrogenic, Androgenic and Thyroid (EAT) hormone systems and that further testing is not needed.