Screening-level Biomonitoring Equivalents for tiered interpretation of urinary 3-phenoxybenzoic acid (3-PBA) in a risk assessment context
- DOI
- Language of the publication
- English
- Date
- 2017-11-04
- Type
- Article
- Author(s)
- Aylward, Lesa L.
- Irwin, Kim
- St-Amand, Annie
- Nong, Andy
- Hays, Sean M.
- Publisher
- Elsevier
Abstract
3-Phenoxybenzoic acid (3-PBA) is a common metabolite of several pyrethroid pesticides of differing potency and also occurs as a residue in foods resulting from environmental degradation of parent pyrethroid compounds. Thus, 3-PBA in urine is not a specific biomarker of exposure to a particular pyrethroid. However, an approach derived from the use of Biomonitoring Equivalents (BEs) can be used to estimate a conservative initial screening value for a tiered assessment of population data on 3-PBA in urine. A conservative generic urinary excretion fraction for 3-PBA was estimated from data for five pyrethroid compounds with human data. Estimated steady-state urinary 3-PBA concentrations associated with reference doses and acceptable daily intakes for each of the nine compounds ranged from 1.7 μg/L for cyhalothrin and deltamethrin to 520 μg/L for permethrin. The lower value can be used as a highly conservative Tier 1 screening value for assessment of population urinary 3-PBA data. A second tier screening value of 87 μg/L was derived based on weighting by relative exposure estimates for the different pyrethroid compounds, to be applied as part of the data evaluation process if biomonitoring data exceed the Tier 1 value. These BE values are most appropriately used to evaluate the central tendency of population biomarker concentration data in a risk assessment context. The provisional BEs were compared to available national biomonitoring data from the US and Canada.
Plain language summary
Biomonitoring efforts have produced continually expanding databases of the levels of chemicals that have been measured in the blood and/or urine of Canadians. Such biomonitoring surveys provide a wealth of information on the levels of chemicals that are found within the general population; however, the presence of a chemical within the body does not necessarily indicate there is the potential for harm. A concept known as Biomonitoring Equivalents (BE) has been developed to aid in interpreting and communicating biomonitoring results in the context of potential risks to health. A BE is defined as the concentration of a chemical in blood or urine that corresponds to an exposure guidance value, such as a reference dose (RfD) or tolerable daily intake (TDI). By comparing biomonitoring data for a chemical with its BE, one can assess whether population exposures to the chemical are below or above a level that is not considered to be harmful. In order to inform Health Canada’s pyrethroid pesticides risk assessment, this study reviewed several available health-based exposure guidance values of pyrethroid pesticides and calculated BE values in urine for 3-Phenoxybenzoic acid (3-PBA), its common metabolite but non-specific biomarker of exposure to a particular pyrethroid. However, a tiered assessment approach using BEs can estimate the safest 3-PBA level in urine. The approach would derive a BE of 3-PBA either based on the most potent form of pyrethroid or the combined exposure levels of all pyrethroids. BEs were estimated for pyrethroid pesticides with human data and ranged from 1.7 ug/L for cyhalothrin and deltamethrin to 520 ug/L for permethrin. In a Tier 1 most potent substance approach, the lowest BE urine level of 1.7 ug/L would be adequate. Whereas a Tier 2 total exposure substance approach, a combined BE of 87 ug/L of 3-BPA in urine was derived by considering the amount of exposure of each pyrethroid into the environment. The geometric mean 3-PBA concentrations in recent US and Canadian population biomonitoring surveys did not exceed the Tier 1 BE values; 95th percentile values were above the Tier 1 value, but 10-fold below the Tier 2 BE value. The outcome of this work will allow Health Canada to place the results of pyrethroid pesticide biomonitoring studies into a public health risk context and will assist in the prioritization of any further risk assessment or management follow-up actions. This study was conducted in collaboration with Summit Toxicology, LLP.
Subject
- Health,
- Health and safety