Guidance on Light-Dependent Peroxidizing Herbicides: Use of the Molar Threshold Value for Adjusting Fish Chronic Endpoints to Account for Ultraviolet Light-enhanced Toxicity

EPA has developed the following guidance for light-dependent peroxidizing herbicides (LDPHs) and other chemicals that may act via a light dependent peroxidizing (LDP) mode of action.

The purpose of this guidance is to assist risk assessors in: (1) identifying herbicides and other pesticides that may act through a LDP mode of action; and (2) applying a molar threshold to fish chronic toxicity test endpoints in the absence of chemical-specific data to account for ultraviolet (uV) light-enhanced toxicity.

• Guidance on Light-Dependent Peroxidizing Herbicides 2016 (pdf) (851.21 KB, June 29, 2016)
  Certain herbicides have been shown to exhibit enhanced toxicity to fish in the presence of ultraviolet light compared to toxicity observed under standard laboratory lighting. This class of herbicides is called light-dependent peroxidizing herbicides (LDPHs). To address concerns that standard laboratory tests may underestimate the toxicity of LPDHs in shallow, clear waters, EPA has developed guidance for identifying and evaluating these pesticides.