UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 WASHINGTON, D.C. 20460

OFFICE PREVENTION, 

PESTICIDES AND TOXIC SUBSTANCES 

MEMORANDUM December 05, 2012

SUBJECT: Ecotoxicity Scoping Document for Gibberellins Registration Review Decision 

Document. 

EPA Reg No.: 62097-

Registration Review 

Case#: 4110

CAS No.: 77-06-5

PC Code: 043801; 043802; 116902.

FROM: Michael Rexrode, Ph.D., Senior Biologist /s/ 12/05/2012

Biochemical Pesticides Branch

Biopesticide & Pollution Prevention Division (7511P)

TO: Menyon Adams, Regulatory Action Leader 12/05/2012

Biochemical Pesticides Branch

Biopesticide & Pollution Prevention Division (7511P)

ACTION REQUESTED

The following is an ecotoxicity assessment for gibberellic acid in support of the Registration 

Review Work Plan. 

RECOMMENDATIONS AND CONCLUSIONS

Executive Summary

The following compounds will be considered collectively as Gibberellic acids (GA): Gibberellic 

acid (GA3) and related isomers known as gibberellins (GA4 and GA7). Gibberellic acids were 

first identified in Japan in 1935, as the metabolic byproduct of a fungal plant pathogen 

Gibberella fujikuroi. Since its discovery, GAs have been found in all plants and have been used 

in agriculture as plant regulators to stimulate cell division and elongation that affects leaf, stem 

and fruit development. In addition to growth stimulation, gibberellic acids can hasten plant 

maturation and seed germination (Feng et al., 2008). 
GA stimulates the cells of germinating seeds to produce mRNA molecules that code for 

hydrolytic enzymes. Since GA regulates growth, applications of very low concentrations can 

have a profound effect while higher concentrations will have the opposite effect; therefore, the 

compounds are usually used in concentrations between 0.01 and 10 mg/L. GA is also widely

used in the grape-growing industry as a hormone to induce the production of larger bundles and 

bigger grapes, especially Thompson seedless grapes (Univ. Davis website).

Based on a review of all available ecological data, exposure information, and gibberellic acids 

non-toxic mode of action, the Agency expects that label rate application of this plant growth 

regulator will pose minimal risk to nontarget wildlife and fish. The rational for this conclusion is 

as follows: 1) Gibberellic acid is produced in all plants as a growth stimulator; 2) Gibberellic

acid is found in algae and seaweed that are natural components of fish diets; 3) Gibberellic acid 

is non-toxic to mammalian and avian species (LD50 > 2,250 mg/kg); 4) A review (11/27/12) of 

the Agency Environmental Incident Information System (EIISv2.1.1; 2012) showed that there 

were no reports of adverse effects from gibberellic acid exposure to non-target species. Data 

waivers were also granted for Nontarget Insect Testing (885.4340) and Nontarget Plant Testing 

(885.4300) in July of 1995 as part of the RED development process because of the unique 

characteristics of this product, its non-toxic mode of action, low use volumes (< 2g/A), and 

biodegradability (low to no persistence). Based on the current use patterns and label directions, 

the non-toxic effects to terrestrial and aquatic plants and animals, the Agency finds that 

Gibberellic Acid use is a No Effect to endangered plant and animal species. 

Figure 1.0 Gibberellic Structure 
Method and Rates of Application:

Gibberellic Acid (GA ) may be applied by aircraft, irrigation systems, ground spray equipment, 

seed treatment or soil incorporation.

Chemical and Fate Properties

Table 1.0 shows that gibberellic acid is very water soluble (4,280 mg/L), has a very low potential 

for bioaccumulation (Log P = 0.72), is non-persistent (DT50 = 3.4 days soil; DT50 = 27 days 

hydrolysis), and photo degrades rapidly (DT50 = 0.2 days).

 Table 1.0 Chemical and Fate Properties for Gibberellic Acid1

OPPTS Guideline No. Property Description of Result

830.6302 Color White

830.6303 Physical State White crystalline solid

830.7200 Melting point/Range Decomposes before melting

830.7220 Boiling point/Range Decomposes before boiling

830.7300 Bulk density (g/ml)/Specific gravity 1.49

830.7550

830.7560

830.7570

Partition Coefficient (nOctanol/Water)P = 5.25 

Log P = 0.72

830.7840 Water Solubility 4,280 mg/L at 200 C

830.7950 Vapor Pressure 0.1 mm Hg @ 25°C 

830.7370 Dissociation constant at 250 C pKa = 4.0

835.3300 Aerobic Soil Degradation (days) DT 50 = 3.4

835.2240 Aqueous Photolysis (Days at pH 7) DT50 = 0.2

835.2130 Aqueous Hydrolysis (days at 200 C pH 7) DT50 = 27

1 BPBD : biopesticide data base University of Hertfordshire

Aquatic Risk Assessment

The available aquatic data shows that gibberellic acid is practically non-toxic to fish (rainbow 

trout LC50 > 150 ppm) and aquatic invertebrates (Daphnia magna LC50 > 143 ppm) (Table 2.0).

Table 2.0 Gibberellic Acid Aquatic Toxicity Data

Test Results MRID

Freshwater Fish LC50 (Trout)

850.1075

LC50 > 150 ppm;

NOEL = 143 ppm

Practically non-toxic

42167401

Freshwater Invertebrate (Daphnia)

850.1010

LC50 > 143 ppm

NOEL = 143 ppm

Practically non-toxic

42084402

In order to assess any potential risk to aquatic life from runoff to an aquatic area, the Agency has 

evaluated the potential for risk through a Tier I single event model, (Parker et al., 1995)

GENEEC (GENeric Estimated Exposure Concentration). This model assumes that one single 

large rainfall/runoff event occurs that removes a large quantity of pesticide from a field to an 

adjacent body of water at one time. Longer-term, multiple-day average concentration values are 

calculated based on the peak day value and subsequent values considering degradation processes.

Table 3.0 shows the estimated environmental concentrations (EECs) that could be expected from 

a worst case (0.5221 lbs ai/A) runoff event from a blueberry field into an aquatic area. The 

Agency calculated risk quotients (RQ) as an exposure/hazard ratio in order to determine the

potential ecological risk from gibberellic acid exposure to non-target aquatic species. Assuming 
that the fish LC50 is = 150 ppm and that the invertebrates EC50 =143 ppm, the respective RQ 

values were found to range from 0.00 – 0.0002 ppm. These projected RQs are below the 

Agency’s level of concern (LOC) (0.05 – 0.5) for risk to non-target aquatic organisms, as well 

as, aquatic endangered/threatened species (Appendix A). The acute risk from gibberellic acid

exposure to non-target and listed aquatic organisms is low.

Table 3.0 GENEEC Version 1.0 Estimated Environmental Concentrations Calculated for 

Gibberellic Acid Runoff (PPM) from a Blueberry Field after a Maximum Application of 

0.52911 lbs. ai/A, one Applications/Years

Peak 

EEC

RQ 

values

Max. 4 

day 

average 

EEC

RQ 

values

Max. 21 

day 

average 

EEC

RQ 

values

Max. 60 

day 

average 

EEC

RQ 

values

Max. 90 

day 

average 

EEC

RQ 

values

0.031 0.0002 0.027 0.0002 0.016 0.00 0.007 0.00 0.004 0.00

Terrestrial Risk Assessment

The acute terrestrial toxicity profile for gibberellic acid shows that this compound is practically 

non-toxic to mammalian (LD50 > 5,000 mg/kg) and avian species (LD50 >2,250 mg/kg; LC50 > 

4,640 mg/kg), as well as, non-target insects (Table 4.0). 

Table 4.0 Gibberellic Acid Terrestrial Toxicity Data

Test Results MRID

Rat Acute Oral 

870.1100

LD50 > 5,000 mg/kg 00153783

Avian Acute Oral (Bobwhite Quail)

850.2100

LD50 > 2,250 mg/L;

Noel +2,250 mg/L

Practically non-toxic

42084401

Avian Dietary (Bobwhite Quail) 

850.2200

LC50 > 4,640 ppm

Practically non-toxic

00121075

Non-target Insects Non-toxic to honey bees 

> 25 ug/bee

43370201

In order to quantitatively evaluate the potential for toxic exposure of gibberellic acid residues to 

avian and mammalian organisms, the Agency used a worst case agricultural scenario on 

blueberries along with mammalian toxicity and avian toxicity data. Using the Terrestrial Residue 

Exposure Model (T-REX) Version 1.4.1. in order to calculate expected residues, the Agency

performed a terrestrial risk assessment that included numerous calculations of dietary exposure 

for multiple weight class animals (Appendix B). Expected residues were calculated for avian and 

mammalian food items along with dissipation rate of a chemical applied to foliar surfaces (single

application) in order to estimate acute and chronic RQs relative to weight class for various sized 

birds and mammals. The upper bound (Table 5.0) Kenega values show that exposure to 

gibberellic acid (0.5291 lbs/A ai) has a low potential for toxic impact to birds (RQ = 0.00 – 0.09) 

and mammals (RQ= 0.00- 0.01) that may be feeding in the area of application. The low toxic risk 

of gibberellic acid to terrestrial organisms, the short environmental half life (4 days) and an 

understanding of the ubiquitous nature of gibberellic acid (produced in all plants) show that there 

is a very low potential for toxic risk to birds and mammalian species, including listed species.
Table 5.0 T-REX Estimated Environmental Concentrations and RQ Values for Gibberellic 

Acid Application to a Blueberry Field after a Maximum Application of 0.52911 lbs. ai/A, 

one Applications/Years

Dose-Based 

Mammalian Classes and Body Weight (grams)

 15 35 1000

EEC RQ EEC RQ EEC RQ

Short grass 121.07 0.01 83.68 0.01 19.40 0.01

Tall grass 55.49 0.01 38.35 0.00 8.89 0.00

Broadleaf 

plants

68.10 0.01 47.07 0.01 10.91 0.00

Fruit/pods 7.57 0.00 5.23 0.00 1.21 0.00

Arthropods 47.42 0.00 32.77 0.00 7.60 0.00

Seeds 1.68 0.00 1.16 0.00 0.27 0.00

Dose-Based

Avian Classes and Body Weight (grams)

 20 100 1000

EEC RQ EEC RQ EEC RQ

Short grass 144.62 0.09 82.47 0.04 36.92 0.01

Tall grass 66.29 0.04 37.80 0.02 16.92 0.01

Broadleaf 

plants

81.35 0.05 46.39 0.02 20.77 0.01

Fruit/pods 9.04 0.01 5.15 0.00 2.31 0.00

Arthropods 56.64 0.03 32.30 0.02 14.46 0.00

Seeds 2.01 0.00 1.15 0.00 0.51 0.00

Endangered Species

The unique characteristics of gibberellic acid, its non-toxic mode of action, low use volumes, and 

biodegradability (low to no persistence) should minimize the risks to threatened and endangered 

species. The Agency has calculated the potential risk to terrestrial and aquatic species by relying 

on Individual Effects Model Version 1.1 that predicts the chance of individual effect at about 1 

in 294,000 for terrestrial animals (Table 6.0) and 1 in 418,000,000 for aquatic species (Table 

7.0). Based on the ecological toxicity data that has been submitted on the active ingredients, 

there should not be toxic risk to endangered/ threatened species from exposure to the end use 

product. Gibberellic acid should present a No Effect to terrestrial and aquatic threatened or 

endangered species, if used in accordance with approved labeling.

Ecological Effects Summary

Based on a review of all available ecological data, exposure information, and gibberellic acids 

non-toxic mode of action, the Agency expects that applications of this plant growth regulator

will pose minimal to no risk to non-target wildlife and fish. The rational for this conclusion is as 

follows: 1) Gibberellic acid is produced in all plants as a growth stimulator; 2) Gibberellic acid is 

found in algae and seaweed that are natural components of fish diets; 3) Gibberellic acid is nontoxic to mammalian and avian species (LD50 > 5,000 mg/kg); 4) A review (11/27/12) of the 

Agency Environmental Incident Information System (EIISv2.1.1; 2012) showed that there were 

no reports of adverse effects from gibberellic acid exposure to non-target species; 5) Gibberellic 

acid is not toxic to bees (< 25 ug/bee). Data waivers were also granted for Nontarget Insect 
Testing (885.4340) and Nontarget Plant Testing (885.4300) in July of 1995 as part of the RED 

development process because of the unique characteristics of this product, its non-toxic mode of 

action, low use volumes (< 2g/A), and biodegradability (low to no persistence). Based on the 

current use patterns, the non-toxic effects to terrestrial and aquatic plants and animals, the 

Agency finds that Gibberellic Acid use is a No Effect to endangered plant and animal species. 

Reference

BPBD : biopesticide data base University of Hertfordshire

http://sitem.herts.ac.uk/aeru/bpdb/Reports/371.htm

Gibberellin and Flame Seedless Grapes from a University of California, Davis website

Feng, S., Martinez C., Gusmaroli, G., Wang, Y., Zhou, J., Wang, F., Chen, L., Yu, L., IglesiasPedraz, J.M., Kircher, S., Eberhard, S., Fu, X., Fan, L-M., and Deng, X.W. 2008. Coordinated 

regulation of Arabidopsis thaliana development by light and gibberellins. Nature 451:475-479.

Parker, R.D., R.D. Jones and H.P. Nelson., 1995. GENEEC: A Screening Model for Pesticide

Environmental Exposure Assessment in Proceedings of the International Exposure Symposium 

on Water Quality Modeling; American Society of Agricultural Engineers, pp. 485-490; Orlando, 

Florida

U.S. EPA. 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum. 

EPA/630/R-95/002F, April 1998.

U.S.EPA 2004. Individual Effects Chance Model Version 1.1. EFED/OPP/USEPA.

U.S.EPA 2008. Terrestrial Residue Exposure Model (T-REX) Version 1.4.1. 

EFED/OPP/USEPA.
Appendix A GENEEC Model

Table A.1 Gibberellic Acid Residues to an Aquatic Area after One Application to

Blueberries (GENEEC)

INPUT VALUES *

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

 --------------------------------------------------------------------------------------------------------------------------

 .529( .529) 1 1 10.0 4280.0 GRHIFI( 6.6) .0 .0

 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

 ---------------------------------------------------------------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

 --------------------------------------------------------------------------------------------------------------------------

 3.40 0 N/A .20- 24.80 6.00 4.83

 GENERIC EECs (IN MICROGRAMS/LITER (PPB) Version 2.0 Aug 1, 2001

 ---------------------------------------------------------------------------------------------------------------------------

 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY

 GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

 ----------------------------------------------------------------------------------------------------------------------------

 30.74 27.51 15.68 6.72 4.52
Appendix B Gibberellic Acid Residues to Terrestrial Area after One Application to

Blueberries (T-REX) 

Table B.1 T-REX Upper Bound Residues and RQ Calculations for mammalian and Avian 

Exposure to Gibberellic Acid
Chemical Name:

 Use

 Formulation

Application Rate 0.5291 lbs a.i./acre

Half-life 3.4 days

Application Interval 0 days

Maximum # Apps./Year 1

Length of Simulation 1 year

Variable application rates? no

Bobwhite quail LD50 (mg/kg-bw) 2250.00

Bobwhite quail LC50 (mg/kg-diet) 0.00

Mallard duck NOAEL(mg/kg-bw) 0.00

Bobwhite quail NOAEC (mg/kg-diet) 2250.00

5000.00

0.00

0.00

0.00

Kenaga

Values

Short Grass 126.98

Tall Grass 58.20

Broadleaf plants 71.43

Fruits/pods/seeds 7.94

Arthropods 49.74

 Upper Bound Kenaga Residues For RQ Calculation

Dietary-based EECs (ppm)

NOAEL (mg/kg-bw)

NOAEC (mg/kg-diet)

Mammals

LD50 (mg/kg-bw)

LC50 (mg/kg-diet)

gibberellic acid

growth regulator

0

Avian

Endpoints
small mid large

20 100 1000

Short Grass 144.62 82.47 36.92

Tall Grass 66.29 37.80 16.92

Broadleaf plants 81.35 46.39 20.77

Fruits/pods 9.04 5.15 2.31

Arthropods 56.64 32.30 14.46

Seeds 2.01 1.15 0.51

20 100 1000

Short Grass 0.09 0.04 0.01

Tall Grass 0.04 0.02 0.01

Broadleaf plants 0.05 0.02 0.01

Fruits/pods 0.01 0.00 0.00

Arthropods 0.03 0.02 0.00

Seeds 0.00 0.00 0.00

Dietary-based RQs 

(Dietary-based EEC/LC50 or 

Acute Chronic

Short Grass #DIV/0! 0.06

Tall Grass #DIV/0! 0.03

Broadleaf plants #DIV/0! 0.03

Fruits/pods/seeds #DIV/0! 0.00

Arthropods #DIV/0! 0.02

Note: To provide risk management with the maximum possible information,

it is recommended that both the dose-based and concentration-based 

RQs be calculated when data are available

Dose-based EECs 

(mg/kg-bw) 

Avian Classes and Body Weights (grams)

Dose-based RQs 

(Dose-based EEC/adjusted LD50)

RQs

Avian Acute RQs

Size Class (grams)

15 35 1000

Short Grass 121.07 83.68 19.40

Tall Grass 55.49 38.35 8.89

Broadleaf plants 68.10 47.07 10.91

Fruits/pods 7.57 5.23 1.21

Arthropods 47.42 32.77 7.60

Seeds 1.68 1.16 0.27

15 grams 35 grams 1000 grams

Acute Chronic Acute Chronic Acute Chronic

Short Grass 0.01 #DIV/0! 0.01 #DIV/0! 0.01 #DIV/0!

Tall Grass 0.01 #DIV/0! 0.00 #DIV/0! 0.00 #DIV/0!

Broadleaf plants 0.01 #DIV/0! 0.01 #DIV/0! 0.00 #DIV/0!

Fruits/pods 0.00 #DIV/0! 0.00 #DIV/0! 0.00 #DIV/0!

Arthropods 0.00 #DIV/0! 0.00 #DIV/0! 0.00 #DIV/0!

Seeds 0.00 #DIV/0! 0.00 #DIV/0! 0.00 #DIV/0!

Medium mammal Large mammal Dose-based RQs 

(Dose-based EEC/LD50 or 

Small mammal

Dose-Based EECs 

(mg/kg-bw)

(grams)

Mammalian Classes and Body weight