Exposures of Aquatic Organisms to the Organophosphorus Insecticide, Chlorpyrifos Resulting from Use in the United States - Reviews of Environmental Contamination and Toxicology

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mass. A study conducted in Iowa under record high rainfall conditions concluded

that the majority of compound was transported attached to eroded sediment (Cryer

and Dixon-White 1995 ). However, based on a combination of low erosion and avail-

ability of large amounts of residues on cotton foliage for wash-off during storms

simulated soon after application of CPY, Poletika and Robb ( 1994 ) suggested that

the majority of the CPY was transported in the dissolved phase of the runoff in

Mississippi. Thus, both dissolved and adsorbed fractions need to be considered as

transport pathways to surface water.

2

Measurements of Chlorpyrifos in Aquatic Environments

2.1

Chlorpyrifos in Surface Water

The most comprehensive dataset of pesticide concentrations has been compiled

from the USGS National Water-Quality Assessment (NAWQA) Program and the

National Stream Quality Accounting Network (NASQAN). These represent concen-

trations measured from 1992 to 2010 (Martin and Eberle 2009 ; Martin et al. 2011 ).

Both NAWQA and NASQAN programs utilized similar methods to collect and pro-

cess samples. Pesticide concentrations were determined by the USGS National

Water Quality Laboratory (NWQL) by using gas chromatography/mass spectros-

copy (GC/MS) in selective ion monitoring (SIM) mode. The USGS determined and

applied a consistent minimum concentration as a bias correction to account for

changes in recovery and limit of detection (LOD) 1 during the sample collection

period. A consistent method of rounding was applied to concentration values and

quality control (QC) samples were removed from the data file before analysis. To

allow for trend analysis, USGS added an attribute to the database to allow users to

create a subset of the data that had no more than one sample per calendar week to

avoid weighting the analysis toward periods of more frequent sampling.

The dataset reported by Martin et al. ( 2011 ) was characterized based on the per-

cent of samples that contained detectable CPY. Characterization also included cal-

culating 90th, 95th, and 99th centile concentrations and maximum concentrations

for all samples. Data were categorized by year, Farm Resource Region 2 (FRR; 9

total), and drainage basin land-use class (4 total). The basin land-use classes were

agricultural (>50% agricultural and ≤5% urban), undeveloped (≤25% agricultural

and ≤5% urban); urban (>25% urban and ≤25% agricultural); and mixed (all other

combinations of urban, agricultural, and undeveloped land). To examine the effect

of the 2001 ban on retail sales of CPY on measured concentrations, data for 1992-

2001 and 2002-2010 were characterized separately.

1 Level of detection (LOD) level of quantitation (LOQ) and method detection limit (MDL) are used

as defined by MacDougall and Crummet (1980).

2 A map and explanation of USDA's Economic Research Service (ERS) Farm Resource Regions is

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