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Project: Development of Toxicity Identification Methods for Current-use Pesticides

Background and Objectives

Identifying the constituents responsible for sediment toxicity is an important management endpoint for activities like site remediation, regulatory compliance, and total maximum daily load establishment. Toxicity identification evaluation (TIE) is a sequence of laboratory investigations used to help determine the cause of toxicity. Standardized TIE methods are available for water samples, but fewer methods are available for sediments, especially those in marine habitats. Moreover, the reliability and specificity of the sediment methods are poorly understood. Recent TIE studies by SCCWRP have implicated organic contaminants as a probable cause of toxicity at several sites in southern California, and suggest that current-use pesticides, such as pyrethroid pesticides, may be the primary cause for toxicity. However, it is difficult to confirm these findings because many other contaminants are present in the samples, and the specificity of TIE methods for pyrethroid pesticides is uncertain.

The goal of this project was to develop and refine TIE methods for current-use pesticides in marine sediments. This goal was addressed through two types of activities: 1) laboratory method development with spiked water and sediment samples; and 2) application of the methods to field sites containing toxic sediments.

The use of pesticides such as fipronil and pyrethroids in southern California has increased dramatically in recent years as the use of organophosphate pesticides has been phased out.


This project was initiated in 2007 and completed in 2010.


Several methods used in freshwater TIEs were refined for use with marine sediments. The methods included treatments that have specific effects on the toxicity of pyrethroids, such as the addition of piperonyl butoxide (PBO; metabolic inhibitor that increases pyrethroid toxicity) and carboxylesterase (enzyme that accelerates pyrethroid degradation in water). The effectiveness of the treatments was evaluated by measuring changes in sediment toxicity to amphipods (Eohaustorius estuarius) relative to baseline samples (no treatment). Laboratory studies were conducted to optimize the effectiveness of these treatments for use on marine pore water and sediment samples. These methods were then used to evaluate toxic sediments at several sites, including the Ballona Creek Estuary. The chemical concentration of pyrethroids and other current-use pesticides (e.g., Fipronil) were measured in order to confirm the TIE results.


Studies at Ballona Creek Estuary indicated that pyrethroid pesticides were a significant contributor to sediment toxicity in the area. Both whole sediment and pore water TIE experiments showed patterns of response that are characteristic of nonpolar toxicants such as pyrethroids. These responses included a reduction in toxicity following treatments to bind or remove nonpolar contaminants and an increase in toxicity following the addition of PBO. Chemical analysis confirmed the preliminary TIE results. Several pyrethroids were present at multiple stations in the estuary and the concentrations were above levels reported to be toxic to amphipods.

Several TIE treatments were applied to whole sediment samples from Ballona Creek Estuary, as well as samples diluted with clean sediments, to produce 25-50% test sediment (shown by coloration). The control consisted of uncontaminated sediments from Oregon and no TIE treatment. The blanks contained control sediments with TIE treatment to check for interferences. Results showed a decrease in toxicity to E. estuarius following carbon (powdered charcoal) addition, and an increase in toxicity (decrease in survival) in the presence of piperonyl butoxide (PBO), a pesticide synergist.


This project was conducted in collaboration with the City of Los Angeles Watershed Protection Division.


Identification of Toxicants in Ballona Creek Sediments (Video) - January 2010 presentation to SCCWRP member agencies describing the TIE approach and results from Ballona Creek Estuary.

For more information on Development of Toxicity Identification Methods for Current-Use Pesticides, contact Keith Maruya at (714) 755-3214.
This page was last updated on: 7/1/2014