Best Use of Available Information in 

Endangered Species Assessments: 

Proposed Approaches with Illustrative Examples

Joy Honegger, Ph.D.

Monsanto Company

April 22, 2014

1
Assessing Taxa for which Toxicity 

of the Pesticide of Interest is Low

2
Selection of Effects Endpoint for Action Area

Indeterminate LD50/LC50

• Interim Approach for Acute Effects for Animals:

– LD50/LC50 of most sensitive species or 

HC05 of SSD of LD50/LC50’s

– Using slope of dose response curve calculate concentration (or 

dose) that would result in a 1 in a million chance of causing 

mortality to an individual. 

• However, when toxicity to a taxon is low:

– LD50/LC50 may be an indeterminate “>” value 

 (little to no mortality at highest dose tested) 

– No slope from a dose response curve available to calculate 1 in a 

million chance 

– However, a NOEL/NOEC may be available from the study indicating 

that No Effect would be expected at highest Estimated 

Environmental Concentration and this information should be 

utilized in the assessment

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Proposal for Taxa for which Toxicity of 

Pesticide of Interest is low

• Establish different criteria for NOEL/NOEC than 

required when a dose response curve and 

calculated LD50/LC50 are available

– Considers the different impact of the two endpoints

– Avoids unnecessary additional vertebrate or 

invertebrate testing

• If NOEL or NOEC for all tested species in a taxon is 

> Highest relevant EEC

– Remove taxa from further consideration of proximity 

to pesticide use

– Conclude “No Direct Effects”

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Example

Pesticide with Low Toxicity to Specific Taxa

• Avian LD50 > 3000 mg/kg bw 

– only adverse observation transient lethargy

• NOEL = 1500 mg/kg bw

• Maximum Use Rate 1.5 lb a.i./A 

– Single Application

• Dose-based EEC for 20 g bird consuming short grass = 

410 mg/kg bw

• NOEL (1500 mg/kg bw) > EEC (410 mg/kg bw)

• Proposed conclusion: 

– No Direct Effects 

– No Proximity Assessment Required

5
Use of Biological Data to Facilitate 

Indirect Effects Assessment 

for a Herbicide

6
Biological Data Available

• Information available on T & E species

– Species characteristics 

– Diet

– Habitat

– Primary Constituent Elements

• This information could be categorized to 

efficiently exclude species from consideration 

of indirect effects

7
Flowchart for Evaluating 

Herbicide Indirect Effects

Proximity * of Listed Species to 

Relevant Land Use in County 

with Crop of Interest?

Review Species-Specific Habitat 

and Diet Requirements 

Yes

No Indirect Effect 

No

Listed Species Plant Dependent 

or Plant Obligate?

Species-County 

Co-occurrences of Listed Species 

and Crop Identified

No

Consider herbicide properties to 

determine if type of plants 

required, for purpose required, 

may be affected

Yes (or 

Potentially)

* Proximity Distance based on Indirect Effect “no effect” distance from application area.

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Flowchart for Evaluating 

Herbicide Indirect Effects -2

Consider herbicide properties to determine if

type of plants required, for purpose required,

may be affected

No Indirect Effect 

Yes No

Subsequent Evaluation to 

Determine if Herbicide 

Use Limitations are 

Needed

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Example for Assessing Indirect Effects 

from Selective Herbicides

• For a herbicide with only post-emergence 

activity

If at drift rates:

Lowest Monocot EC25 > EECdrift, field edge

Lowest Dicot EC25 < EECdrift, field edge

But perennial species (e.g. brush and trees) are 

 not affected at drift rates

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Selective Herbicide Indirect Effects Example

Habitat/Diet/Repro Requirements Evaluation

• Review species requirements for habitat, diet & 

reproduction

– If no plant requirements, conclude “No Indirect 

Effect”

– If plants required, review nature of requirement

• If monocot required – Conclude “No Indirect Effect”

• If tree or brush required – Conclude “No Indirect 

Effect”

• If other dicot required – Consider if requirement is 

– For dicots in general - use EC25 in further evaluation 

– For specific plant species – use NOEC in further evaluation

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Species Diet and Habitat Examples

Species

Primary

Feeding

Strategy

Feeding Ecology Habitat Description

Least tern

(Sternula

antillarum)

Piscivore

Invertivore

Eats mainly small 

fishes (generally less 

than 9 cm long), 

sometimes 

crustaceans or 

insects.

Seacoasts, beaches, bays, estuaries,

lagoons, lakes, and rivers. Nests usually in

shallow depression on level ground on

sandy or gravelly beaches and banks

of rivers or lakes, typically in areas

with sparse or no vegetation

Marbled Murrulet

(Brachyramphus

marmoratus)

Invertivore, 

Piscivore

Diet includes fishes 

(sandlance, capelin, 

herring, etc.), 

crustaceans (mysids, 

euphausiids), 

mollusks

Old growth coastal forests

Mount Graham Red 

Squirrel

(Tamiasciurus

hudsonicus

grahamensis)

Frugivore, 

Granivore

Diet consists of seeds, 

conifer cones, nuts, 

fruits. Occasionally 

feeds on 

invertebrates and 

small vertebrates

Major constituent element is dense stands 

of mature spruce-fir forest

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Use of Biological Data

• A database of biological data relevant for the 

assessment of indirect effects should be 

developed

– Categorize species according to classes of taxa

required for diet, habitat, temporal relationships, 

etc.

– Allow efficient sorting and evaluation of species 

requiring indirect effects assessment

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