UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C., 20460
                                   OFFICE OF
                   CHEMICAL SAFETY AND POLLUTION PREVENTION
                                       
                                                                               


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 fluoro-complexes (at acidic pH), hydroxyl-aluminum (at environmental pH), and fluorhydric acid.   


EPA Response:  The introduced F[-], Al[3+], 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 hydroxyl-aluminum 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 fluoro-complex (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.

                                       

Figure 1: Mole Fraction Diagrams for Al[3+] and fluoro-complexes and hydroxyl-aluminum complexes. (Equilibrium conditions assumed are log (SO4[2-])=-4 M.  Top Graph)  No F- precipitation 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 Al[3+] 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 Al[3+] 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 F- and Al[3+] 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.  

                                       


                                       
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  F[-] and Al[3+] concentrations in ambient waters.  The median concentration of detectable F[-] and Al[3+] 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 aquatic-phase 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 Al[3+] 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 Al[3+] 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 two-generation rat study; MRID 43387501).  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 Al[3+] 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.


