OFFICE OF

CHEMICAL SAFETY AND 

POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C., 20460

September 20, 2011

MEMORANDUM

Subject: Response to Comments on the Preliminary Problem Formulation for the 

Ecological Risk and Drinking Water Exposure Assessments for Cryolite (PC 

Code 075101; DP Barcode 383606) 

To: Molly Clayton, Risk Manager Reviewer 

Risk Management and Implementation Branch 3 

Pesticide Re-evaluation Division

From: James Hetrick, Ph.D., Senior Science Advisor

Melissa Panger, Ph.D., Senior Biologist

Dana Spatz, Branch Chief

Environmental Risk Branch 3

Environmental Fate and Effects Division

Office of Pesticide Programs

This memorandum provides a response to public comment on the Registration Review

Preliminary Problem Formulation for the Ecological Risk and Drinking Water Exposure

Assessments for Cryolite (PC Code 075101; DP Barcode 383606). Comments were received

from the Fluoride Action Network (FAN) (7/5/11). The comments will be addressed according

to topic headings in the comment document.

3.4.1. OPP should require that testing for adverse effects include cryolite and all of its

degradation products and complexes.

FAN Comment: The FAN believes that cryolite use will elevate the aluminum and fluorine 

concentrations to levels of toxicological concern. They contend the Agency did not adequately 

address the environmental chemistry of aluminum. Additionally, they believe the synthetic 

cryolite is chemically different than natural cryolite due to the presence of impurities including 

aluminum oxide, aluminum fluoride, lithium fluoride, magnesium fluoride, calcium fluoride, 

quartz, and iron oxide. They reference MSDS data sheets stating degradation of fluorocomplexes (at acidic pH), hydroxyl-aluminum (at environmental pH), and fluorhydric acid. 
EPA Response: The introduced F-

, Al3+, and Na+from cryolite dissolution will be incorporated 

into the natural biogeochemical cycles in the soil and aquatic environments. Mechanisms 

controlling environmental concentrations of F-, Al 3+, and Na+ include sorption, mineral 

precipitation, and ligand complexation. The formation of fluoro-complexes and hydroxylaluminum complexes will occur regardless of the application of cryolite. These complexes occur 

naturally in soil and water environments. The relative proportion of the fluoro-complexes is 

highly dependent on the F- concentration. In the absence of fluoride precipitation, the fluorocomplex (AlF3) is the predominate inorganic Al complex. However, the precipitation of fluorite 

(CaF2) changes the distribution of fluoro-complexes and hydroxyl-aluminum complexes. The 

fluoro-complexes are only predominate in acidic environments (pH<6.4). In near neutral and 

alkaline environments (pH>6.4), the hydroxyl-aluminum complexes Al(OH)3 and Al(OH)4

-

 are 

predominate. These data indicate the fluoro-complexes of aluminum should be important in 

acidic environments.

pH

3 4 5 6 7 8 9

Mole Fraction

0.0

0.2

0.4

0.6

0.8

1.0

 Al3+ 

 AlOH+2 

 Al(OH)2+ 

 Al(OH)3 

 Al(OH)4- 

 AlF+2 

 AlF2+ 

AlF3 

 AlSO4+ 

pH

3 4 5 6 7 8 9

Mole Fraction

0.0

0.2

0.4

0.6

0.8

1.0

Figure 1: Mole Fraction Diagrams for Al3+ and fluoro-complexes and hydroxyl-aluminum 

complexes. (Equilibrium conditions assumed are log (SO4

2-

)=-4 M. Top Graph) No Fprecipitation assumed. Bottom Graph) Fluorite precipitation assumed.
As stated in the problem formulation, the incremental addition of cryolite is not expected to 

cause elemental exceedance of natural background concentrations, especially for aluminum and 

sodium (Table 1). More importantly, chemical equilibrium in soil and aquatic environments is 

expected to buffer concentrations of Al3+ and F-. 

Table 1. Relative contribution of elemental components from cryolite application to soil. 

Elemental 

Components

Elemental

Fraction

Elemental 

Maximum

Application Rate

(lbs/A)1

Elemental 

Maximum

Application Rate

(mg/kg)2

Average 

Elemental 

Concentration in 

Soil

(mg/kg)

Al 0.13 19.97 9.985 71000

F 0.55 84.48 42.24 200

Na 0.32 49.15 24.58 6300

The chemistry of Al3+ in soil solution is controlled by the aluminum oxide minerals (Lindsay, 

1979). In contrast, the fluoride concentration in soil solution may be controlled by fluoride

minerals such as fluorite (CaF2), fluorphlogopite (KMg3AlSi3O10F2), and fluoroapatite 

(Ca5(PO4)3F). Figure 2 illustrates that free ion concentrations of Fand Al3+ from cryolite 

dissolution in soil will be supersaturated to fluorite and gibbsite (γ-AlOH3). ). From a single 

application of cryolite, the theoretical soil solution concentration of total fluoride and aluminum 

is 0.01111 moles/liter (210 mg/L) and 0.00185 moles/liter (49.91 mg/L). Thermodynamic 

equilibrium will cause precipitation of the dissolved fluorite and gibbsite in soils. 
pH

2 3 4 5 6 7 8 9 10

log(F

-

)

-10

-8

-6

-4

-2

0

Fluorite-Soil Ca 

Fluorite-CaCO3 (0.003 M CO2) 

Fluorite-CaCO3 (0.0003 M CO2) 

 Theoretical Soil Fluoride Concentratio

 Soil Solution Fluoride Concentration 

Supersaturation

Supersaturation

pH

3 4 5 6 7 8 9

log(Al

3+

)

-20

-15

-10

-5

0

5

Amorp Al(OH)3 

 Gibbsite 

 Theoretical Soil Solution Al3+ Concentration 

Supersaturation

Figure 2: Mineral Stability Diagrams with Theoretical Soil Solution Activity of F- and Al3+ 

from a Single Cryolite Application 

A review of NAWQA water quality data provides an indication of Fand Al3+ concentrations in 

ambient waters. The median concentration of detectable F

-

and Al3+ in NAWQA samples (2000-

2010) was 0.241 mg/L (n=7574 samples) and 5.89 ug/L (n=1274 samples), respectively. These 

data illustrate the background concentration in the surface waters.

3.4.5. (in the summary; “3.5.5.” in the text). OPP has failed to include amphibians in the 

Ecological Risk Assessment.

FAN Comment: As described in the cryolite Problem Formulation, OPP uses a surrogate 

approach in its ecological risk assessments (i.e., OPP assumes that toxicity to birds is similar to 

terrestrial-phase amphibians and reptiles and that cryolite toxicity to fish is similar to aquaticphase amphibians). The FAN states that these toxicity assumptions “... ignore that amphibians 
have been shown to be extremely sensitive to toxins, and are considered ‘valuable indicators of 

environmental stress’ (p. 4, FAN comments, 2011). They state that OPP should require cryolite 

toxicity data on amphibians and conduct a risk assessment for amphibians in the cryolite risk 

assessment conducted for Registration Review. 

EPA Response: As discussed in the response to 3.4.1. above, the incremental addition of 

cryolite is not expected to cause elemental exceedance of natural background concentrations, 

especially for aluminum and sodium, in soil or water. More importantly, chemical equilibrium 

in soil and aquatic environments is expected to buffer concentrations of Al3+ and F-. As a result, 

exposure to amphibians to aluminum, fluorine or sodium from cryolite use, either via contact 

with soil or in the aquatic environment, is not expected to exceed normal background levels for 

these elements. Therefore, additional toxicity data using amphibians would not likely alter 

cryolite risk conclusions. Therefore, EFED does not recommend requesting toxicity data on 

amphibians for the cryolite ecological risk assessment conducted for Registration Review. 

3.4.6. (in the summary; “3.5.6.” in the text). OPP should require reproductive/developmental 

toxicity/teratogencity testing for terrestrial and aquatic species.

FAN Comment: “OPP assumes that because cryolite is “practically nontoxic to avian species 

on an acute oral and sub-acute dietary basis” and is “no more than slightly toxic to small 

mammals on an acute oral basis” (EPA OCSPP, 2011a, p. 13) that chronic risk to birds and small 

mammals is not expected. However, it is well known that the developing embryo and fetus is 

much more vulnerable to toxins than is the adult form. Furthermore, for all but mammalian 

species, acute exposure of the female at the time of ovulation and fertilization potentially

establishes a situation of chronic exposure for the duration of embryological development. Thus 

OPP should require reproductive/developmental toxicity/teratogenicity testing for all 

representative terrestrial and aquatic species exposed to cryolite and all of its degradation 

products and complexes.”

EPA Response: As discussed in the response to 3.4.1. above, the incremental addition of 

cryolite is not expected to cause elemental exceedance of natural background concentrations, 

especially for aluminum and sodium, in soil or water. More importantly, chemical equilibrium 

in soil and aquatic environments is expected to buffer concentrations of Al3+ and F-. 

Therefore, additional toxicity data using aquatic animals would not likely alter cryolite risk 

conclusions. Therefore, EFED does not recommend requesting additional toxicity data on 

aquatic animals for the Registration Review ecological risk assessment for cryolite. 

EFED, however, does agree that there is a potential for terrestrial animals to be exposed to 

cryolite via ingestion of vegetative dietary items that have been treated with cryolite (either 

directly or via spray drift). Additionally, due to cryolite’s use pattern, there is a potential for 

repeated exposure to cryolite (cryolite can be applied to crops several times per season). 

Therefore, EFED agrees that risk to birds and mammals from chronic exposure via the ingestion 

of contaminated vegetative dietary items should be assessed in the risk assessment conducted for 

cryolite for Registration Review. 
There are currently acceptable reproductive toxicity data available for mammals (a twogeneration rat study; MRID 433875011

). These data will be used in the cryolite ecological risk 

assessment to assess potential risks to mammals from repeated exposure to cryolite. No chronic 

toxicity data for cryolite are currently available for birds. Therefore, to adequately assess risks to 

birds from potential repeated exposure to cryolite, EFED recommends that an avian reproduction 

study (850.2300) be conducted for cryolite.

3.4.7. (in the summary; “3.5.7.” in the text). OPP should require chronic toxicity testing for 

aquatic animals.

FAN Comment: FAN requests that additional toxicity data on aquatic animals (chronic data) be 

conducted due to the potential for chronic exposure to cryolite in aquatic environments due to 

cryolite’s use patterns.

EPA Response: As discussed in the response to 3.4.1. above, the incremental addition of 

cryolite is not expected to cause elemental exceedance of natural background concentrations, 

especially for aluminum and sodium, in soil or water. More importantly, chemical equilibrium 

in soil and aquatic environments is expected to buffer concentrations of Al3+ and F-. 

Therefore, additional toxicity data using aquatic animals would not likely alter cryolite risk 

conclusions. Therefore, EFED does not recommend requesting additional toxicity data on 

aquatic animals for the Registration Review ecological risk assessment for cryolite.

 

1 MRID 43387501. Schroeder, R. E. (1994). A Two-Generation Dietary Reproduction Study in Rats with Kryocide 

(Cryolite). Pharmaco LSR, Inc. Toxicology Services North America, New Jersey 08875-2360.