Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

Exposure and Response Integration
In Figures 39-41, we show the overlap between exposure estimates for the three carbamates and
concentrations that affect assessment endpoints. The figures show the exposure concentration
ranges (minimum – maximum values) gleaned from the three predominant sources of exposure
data we analyzed: monitoring data; EPA’s estimates presented in the BEs that represent crop
uses; and NMFS’ modeling estimates for off-channel habitats. None of the modeled exposure
estimates were derived for non-crop use. This is a major data gap as carbaryl is used extensively
in urban and residential areas. The effect concentrations are values taken from the toxicity data
reviewed in the Response Analysis Section. With respect to the assessment endpoint survival,
recall that the effect concentrations are LC50s, thus death of sensitive individuals is not
represented by this metric and can occur at concentrations well below LC50s. Additionally, we
cannot accurately predict at what concentrations death first occurs because dose-response slope
information was generally not provided for most of the acute lethality studies. Although we are
unable to determine at what concentration an individual organism might die, we do incorporate
survival endpoints from acute 96 h studies using a default slope in a population modeling
exercise discussed below. This slope is recommended by EPA when more relevant information
is unavailable (EPA 2004). Where overlap occurs between exposure concentrations and effect
concentrations NMFS explores the likelihood of adverse effects. If data suggest exposure
exceeds adverse effects thresholds, we discuss the likelihood and expected frequency of effects
based on species information and results of the exposure and response analyses.
This is a coarse analysis because it does not present temporal aspects of exposure nor does it
show the distribution of toxicity values. However, it does allow us to systematically address
which assessment endpoints are affected from carbaryl, carbofuran, and methomyl exposure.
Where significant uncertainty arises, NMFS highlights the information and discusses its
influence on our inferences and conclusions. We discuss the uncertainties related to these
endpoints under associated risk hypotheses later in this section.
Carbaryl
Concentration ranges overlap with most of the assessment endpoint ranges indicating that
adverse effects are expected in salmonids if exposed for sufficient durations (Figure 39). Prey
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