[Federal Register Volume 60, Number 176 (Tuesday, September 12, 1995)]
[Proposed Rules]
[Pages 47334-47337]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-22618]



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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 372

[OPPTS-400098; FRL-4972-8]


Zinc Oxide; Toxic Chemical Release Reporting; Community Right-To-
Know

AGENCY: Environmental Protection Agency (EPA).

ACTION: Denial of petition.

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SUMMARY: EPA is denying a petition to delist zinc oxide from the zinc 
compounds category subject to the reporting requirements under section 
313 of the Emergency Planning and Community Right-to-Know Act of 1986 
(EPCRA) and section 6607 of the Pollution Prevention Act of 1990 (PPA). 
This decision is based on evidence that zinc ion can become available 
from zinc oxide through several mechanisms and that zinc ion can 
reasonably be anticipated to be toxic to aquatic organisms.

FOR FURTHER INFORMATION CONTACT: Maria Doa, Petitions Coordinator, 202-
260-5997, or e-mail: [email protected], for specific 
information regarding this document. For further information on EPCRA 
section 313, contact the Emergency Planning and Community Right-to-Know 
Information Hotline, Environmental Protection Agency, Mail Stop 5101, 
401 M St., SW., Washington, DC 20460, Toll free: 800-535-0202, Toll 
free TDD: 800-553-7672. 

[[Page 47335]]


SUPPLEMENTARY INFORMATION:

I. Introduction

A. Statutory Authority

    This action is issued under sections 313(d) and (e)(1) of the 
Emergency Planning and Community Right-to-Know Act of 1986 (EPCRA), 42 
U.S.C. 11023. EPCRA is also referred to as Title III of the Superfund 
Amendments and Reauthorization Act (SARA) of 1986 (Pub. L. 99-499).

B. Background

    Section 313 of EPCRA requires certain facilities manufacturing, 
processing, or otherwise using listed toxic chemicals to report their 
environmental releases of such chemicals annually. Beginning with the 
1991 reporting year, such facilities also must report pollution 
prevention and recycling data for such chemicals, pursuant to section 
6607 of the Pollution Prevention Act of 1990 (PPA), 42 U.S.C. 13106. 
Section 313 established an initial list of toxic chemicals that was 
comprised of more than 300 chemicals and 20 chemical categories. Zinc 
oxide is a zinc compound reportable under the zinc compounds category 
provided in the initial EPCRA section 313 list of chemicals. Section 
313(d) authorizes EPA to add or delete chemicals from the list, and 
sets forth criteria for these actions. EPA has added and deleted 
chemicals from the original statutory list. Under section 313(e), any 
person may petition EPA to add chemicals to or delete chemicals from 
the list. EPA must respond to petitions within 180 days, either by 
initiating a rulemaking or by publishing an explanation of why the 
petition is denied.
    EPA issued a statement of petition policy and guidance in the 
Federal Register of February 4, 1987 (52 FR 3479), to provide guidance 
regarding the recommended content and format for submitting petitions. 
On May 23, 1991 (56 FR 23703), EPA issued guidance regarding the 
recommended content of petitions to delete individual members of the 
section 313 metal compound categories. EPA has also published a 
statement clarifying its interpretation of the section 313(d)(2) and 
(3) criteria for adding and deleting chemical substances from the 
section 313 list (59 FR 61439, November 30, 1994).

II. Description of Petition and Relevant Regulations

    On April 4, 1995, EPA received a petition from the American Zinc 
Association to delete zinc oxide from the compounds reportable under 
EPCRA section 313 under the zinc compounds category. The petitioner 
contends that zinc oxide is not the type of compound that should be 
reported under EPCRA section 313 because zinc compounds are ``Generally 
Recognized as Safe by the Food and Drug Administration as: a dietary 
supplement (21 CFR 182.5991); a nutrient (21 CFR 182.5991); and a 
resinous/polymeric coating (21 CFR 175.300).'' The petitioner adds that 
``zinc oxide has been used for decades as a skin ointment--e.g., for 
diaper rash--and protectant. * * *''

III. EPA's Technical Review of Zinc Oxide

    The technical review of the petition to delete zinc oxide from the 
zinc compounds category focused on the available ecological and 
environmental fate data. Based on a review of these data, EPA has made 
the determination that there is sufficient evidence to reasonably 
anticipate that zinc ion may cause environmental toxicity and that zinc 
ion can become available in the environment from zinc oxide. The 
principal concern regarding zinc oxide is its toxicity to aquatic 
species and its ability to bioaccumulate. Several mechanisms have been 
identified by which zinc ion can become available in the environment 
from zinc oxide. For example, zinc ion may become available in the 
environment from zinc oxide via dissolution in aqueous solutions.

A. Chemistry

    Pure zinc oxide (ZnO) is typically a white or yellow-white 
amorphous powder. Crystalline zinc oxide has a hexagonal crystal 
structure. Zinc oxide has a reported melting point in the range of 1970 
 deg.C to 1975  deg.C. Zinc oxide is produced by oxidizing zinc vapors 
in burners. The source of the zinc vapor is either impure zinc oxide or 
purified zinc metal. Zinc vapor generated from purified zinc metal will 
provide the highest purity zinc oxide (Refs. 1-4).
    An important conversion in the environment is the conversion of 
zinc oxide to zinc hydroxide. Zinc hydroxide also dissociates in the 
environment to yield zinc ion. Below 39  deg.C, zinc oxide reacts 
slowly with water to form zinc hydroxide (Zn(OH)2). The rate of 
conversion of zinc oxide to zinc hydroxide is dependent on various 
factors, the most important of which is temperature. Above 39  deg.C, 
ZnO is the stable form.
    The reported water solubility of zinc oxide ranges from 1.6 
milligrams per liter (mg/L) (29  deg.C) to 5 mg/L (25  deg.C). The two 
most common forms of zinc hydroxide are the amorphous form and the 
-Zn(OH)2 form. The reported water solubility of zinc hydroxide 
ranges from 2.92 mg/L (18  deg.C) to 15.5 mg/L (29  deg.C). These 
variations in solubility data are most likely due to variations in the 
solubility tests with respect to the form of zinc used, oxide or 
hydroxide (the amorphous form of zinc hydroxide is more soluble), pH, 
temperature, and experimental variability. The solubilities of zinc 
oxide and zinc hydroxide are at a minimum at pH 9.3. At this pH, the 
solubility of zinc hydroxide is 0.0822 mg/L for the amorphous form and 
0.0041 mg/L for the -Zn(OH)2 form. Zinc oxide and 
hydroxide are insoluble in organic solvents, including alcohols and 
acetone (Refs. 3, 5-9).
    Zinc oxide and hydroxide are amphoteric; they dissolve in acids to 
form salts and in alkalis to form zincates. Zinc oxide will dissolve in 
hydrochloric acid, for example, generating zinc chloride (ZnCl2), 
a salt with appreciable water solubility (432 grams (g) ZnCl2 
dissolves in 100 g H2O at 25  deg.C). Common zincates include 
[Zn(OH)4]-2 and [Zn(OH)3]-. Zinc oxide also dissolves in 
ammonia generating the tetraligated complex, [Zn(NH3)4]+2. 
The conversion of zinc oxides to zinc salts is of importance because of 
the high solubility of many of the salts in water which would make the 
zinc ion available (Refs. 1, 2, 10, and 11).
    Although zinc oxide may be poorly reactive under some conditions, 
it is reported that zinc oxide adsorbs carbon monoxide and carbon 
dioxide. Zinc oxide reacts with carbon dioxide in moist air generating 
zinc carbonates, in particular zinc oxycarbonate. The reported water 
solubility of zinc carbonate ranges from 0.01 grams per liter (g/L) (15 
 deg.C) to 0.7 g/L (18  deg.C) (Refs. 1 and 8).
    Zinc oxide completely absorbs UV radiation below 366 nanometer 
(nm), and as a result, is used as a white pigment. A more common use 
for zinc oxide is as an accelerator, activator and stabilizer in rubber 
manufacture (Refs. 1 and 2).

B. Environmental Fate

    The mechanisms that contribute most to the environmental fate of 
zinc oxide are dissolution, sorption, and precipitation, all of which 
are affected particularly by the pH of the media, but also by other 
factors including temperature. Unlike other zinc compounds (such as 
zinc sulfide), zinc oxide does not undergo significant microbial 
transformation.
    1. Water. The solubility of zinc oxide at pH 7 and 29  deg.C is 
approximately 5 to 15 mg/L. Because zinc oxide is amphoteric, it is 
more soluble at pH values other than 7, particularly values less than 
7. Above pH 7, zinc oxide and 

[[Page 47336]]
zinc hydroxide will dissolve to form other zincates. These zinc 
compounds are also amphoteric; the availability of zinc ion from these 
compounds, therefore, is also dependent on their solubility and pH.
    In water, zinc ion may associate or react with neutral or ionic 
compounds to form inorganic salts, stable organic complexes, or 
inorganic or organic colloids. The quantity of zinc ion available in 
water from each of these forms is dependent upon the solubility of 
these forms, pH, temperature, the total amount of the zinc form present 
in water, and the presence of other metal ions, organic compounds, and 
inorganic compounds.
    Zinc ion will eventually adsorb to sediments. The extent to which 
this occurs is strongly dependent on pH, temperature, salinity, and the 
amount of zinc ion present. Below pH 5, minimal soil sorption is 
expected.
    In wastewater treatment plants, zinc oxide is usually removed as a 
solid. Removal rates usually range up to 90 percent. Any solubilized 
zinc oxide will be released to surface water as zinc ion in solution 
with a counter anion in solution.
    2. Land. The movement of zinc oxide in soils is strongly pH 
dependent. At pH 7, zinc ion will be available from zinc oxide in soils 
to the extent that the oxide is solubilized. If the pH falls below 7 in 
soils, leaching of zinc ion will increase due to the increased 
solubility of zinc oxide. Sorption of zinc ion to soils will be minimal 
at pH values less than 5. The sorption of zinc ion to soils, therefore, 
significantly decreases through a critical pH range of 7 to 5. Zinc ion 
not adsorbed to soils will eventually end up in the water column (Ref. 
12).
    3. Air. Zinc oxide may be present in the atmosphere in particulate 
form, originating primarily from dust from manufacturing and processing 
sites. Deposition of particulate zinc oxide by fallout or washout 
generally occurs in a short period of time in the vicinity of the 
emission source.

C. Toxicity Evaluation

    EPA's review primarily addressed the environmental toxicity of zinc 
ion. There is sufficient evidence to indicate that zinc ion may cause 
environmental toxicity. Zinc ion can become available in the 
environment from zinc oxide through several mechanisms. Zinc ion can 
become available from dissolution of zinc oxide in aqueous solution, 
particularly at pH values between 5 and 7. Zinc ion can become 
available from the dissolution or reaction of zinc oxide to produce 
several products of varying solubility, such as zinc hydroxide 
(generated from the hydrolysis of zinc oxide); zincates (generated from 
the dissolution of zinc oxide or zinc hydroxide in alkaline solution); 
zinc salts (including zinc chloride, generated from the dissolution of 
zinc oxide in a hydrochloric acid solution); and zinc carbonates 
(generated from the reaction of zinc oxide with carbon monoxide or 
carbon dioxide in moist conditions).
    Based on the availability of zinc ion, zinc oxide may cause adverse 
environmental effects. In terms of health effects, it should be noted 
that the predominant concern of most literature available on the 
toxicology of zinc ion deals with the effects of zinc ion deficit 
rather than excess. Zinc is classified as an essential nutrient. The 
National Academy of Science recommends a dietary allowance of 0.21 mg 
elemental zinc per kilogram per day (kg/day). Zinc is also an essential 
nutrient to aquatic and terrestrial organisms; it is involved in the 
synthesis of nucleic acids and enzymes.
     Environmental effects (Refs. 13 and 14). By whatever route 
available, zinc ion exhibits high toxicity to aquatic organisms. This 
conclusion is based on a substantial amount of information available 
for zinc ion which includes acute toxicity values lower than 100 parts 
per billion (ppb), and bioconcentration values higher than 1,000. 
Numerous studies indicate that zinc ion also has a high chronic 
toxicity.
    a. Aquatic toxicity. The available evidence indicates that zinc ion 
is highly toxic to aquatic organisms and has a high potential to 
bioaccumulate.
    In natural waters, zinc ion occurs in both suspended and dissolved 
forms. It can exist as a simple hydrated ion; as various inorganic 
salts; in stable organic complexes; or adsorbed into or occluded in, 
inorganic or organic colloids. The quantity of zinc ion available from 
each of these forms is dependent upon pH, temperature, and the total 
amount of the zinc form present in water, and the presence of other 
metal ions or organic and inorganic compounds. Zinc is eventually 
partitioned into sediments. Zinc ion bioavailability from sediments is 
enhanced under conditions of high dissolved oxygen, low salinity, low 
pH, and high levels of humic substances. Zinc ion remaining in 
sediments may be toxic to or bioaccumulate in sediment organisms.
    The levels of acute toxicity for zinc ion to various fish and 
invertebrates range from 40 ppb to 58,100 ppb. This wide range is 
partially due to the hardness of the water used in the studies; 
generally as water hardness increases the acute toxicity of zinc ion 
decreases. The 96-hour LC50 (median lethal concentration) for 
rainbow trout in a flow-through system was 93 ppb. The 96-hour 
LC50 for cutthroat trout was 90 ppb. The 48-hour LC50 value 
for a daphnid species was 40 ppb. Acute toxicity EC50 values of 40 
and 100 ppb were noted in daphnids.
    Numerous other acute tests have been conducted on estuarine and 
marine invertebrates and fish. EC50 values of 310 ppb and 166 ppb 
were calculated by testing oysters and hard shelled clams, 
respectively. EC50 values for a copepod, mysid shrimp, lobster, 
and hermit crab were 210 ppb, 498 ppb, 175 ppb, and 400 ppb, 
respectively. Estuarine and marine fish were less sensitive to zinc ion 
than invertebrates. The LC50 values ranged from 2,730 ppb for 
larvae of Atlantic silversides to 83,000 ppb for larvae of mummichog.
    Zinc ion exhibits high chronic toxicity in the aquatic environment. 
The maximum acceptable toxicant concentration (MATC) in soft water was 
36 to 71 ppb for rainbow trout fry (hatching from unexposed eggs). The 
MATC for fathead minnows, based on spawning and hatching success and 
fry survival, in hard water (200 mg/L as CaCO3) was 30 to 180 ppb. 
The MATC for this fish in soft water was 78 to 145 ppb.
    In invertebrates (Daphnia magna), reproduction was impaired by 10 
percent after a 21-day exposure to 70 ppb zinc ion. Cell growth was 
inhibited in algae (Selenastrum capricornutum) after exposure for 7 
days at a concentration of 30 ppb, and the EC95 for growth after 
exposure for 14 days was 68 ppb.
    Marine algae are very sensitive to zinc. Growth was inhibited in 
kelp (Laminaria hyperiborea) at 100 ppb and in algae (Skeletonema 
costatum) at 50 ppb. Cell numbers decreased in three species of marine 
algae, Gymnodinium splendens, Schroderella schroederi, and 
Thalassiosira rotula, at 100 ppb, 50 ppb, and 100 ppb, respectively.
    b. Bioaccumulation. Zinc ion can reasonably be anticipated to 
bioaccumulate in aquatic organisms. Bioconcentration factors (BCFs) of 
1,130 and 432 were noted in mayflies and flagfish, respectively. BCFs 
for marine algae (Cladophora and Fucus serratus) and oysters were noted 
to be 4,680, 16,600, and 16,700, respectively.

D. Technical Summary

    The technical review of the petition to delete zinc oxide from the 
zinc compounds category focused on the ecological and environmental 
fate data. Based on a review of these data, EPA has made the 
determination that there is 

[[Page 47337]]
sufficient evidence to reasonably anticipate that zinc ion may cause 
environmental toxicity and that zinc ion can become available in the 
environment from zinc oxide. The principle concern regarding zinc oxide 
is its toxicity to aquatic species and its ability to bioaccumulate. 
Several mechanisms have been identified by which zinc ion can become 
available in the environment from zinc oxide (see Unit III.A. and B. of 
this preamble). Zinc ion may become available in the environment from 
zinc oxide via dissolution in aqueous solutions particularly between 
the pH range of 5 and 7.

IV. Rationale for Denial

    EPA is denying the petition submitted by the American Zinc 
Association to delete zinc oxide from the reporting requirements under 
the zinc compounds category of the EPCRA section 313 list of toxic 
chemicals. This denial is based on: (1) The Agency's conclusion that 
zinc ion can become available from zinc oxide, and (2) the 
determination that there is sufficient evidence to indicate that zinc 
ion causes aquatic toxicity. Several mechanisms have been identified 
where zinc ion can become available in the environment from zinc oxide, 
particularly dissolution in aqueous solutions.
    Additionally, zinc oxide and zinc hydroxide may dissolve in acids 
or alkalis to form salts or zincates, respectively. Many zinc salts are 
particularly water soluble, allowing another pathway by which zinc ion 
may become available. Due to these mechanisms, which may result in the 
availability of zinc ion from zinc oxide, zinc oxide contributes to the 
overall loading of zinc ion to the environment.
    EPA has determined that zinc ion can reasonably be anticipated to 
cause a significant adverse effect on the environment of a sufficient 
seriousness to warrant continued reporting of zinc oxide under EPCRA 
section 313 because of zinc ion's high toxicity to aquatic organisms 
and its tendency to bioaccumulate in the environment. Concern regarding 
these effects are in accordance with the criteria in EPCRA section 
313(d)(2)(C). Because zinc oxide can reasonably be anticipated to be 
highly ecotoxic and induce well-established serious adverse effects, 
EPA does not believe that an exposure assessment is necessary to make 
the determination required by EPCRA section 313(d)(2)(C).
    In reference to the petitioner's contention that zinc oxide should 
not be included on the EPCRA section 313 list because zinc compounds 
are ``Generally Recognized as Safe by the Food and Drug 
Administration,'' EPA is not persuaded that this is a sufficient basis 
for removing zinc oxide from the list. While EPA agrees that zinc is 
classified as an essential nutrient and, in terms of human health 
effects, the predominant concern cited in most of the available 
literature deals with the effects of zinc ion deficit rather than 
excess, this is not the whole picture. EPA, in making its listing 
decisions under section 313 of EPCRA, considers a different set of 
issues than those addressed by FDA in its regulatory decisions. 
Specifically, EPA considers the potential for adverse impacts on the 
environment, as well as those on human health. As indicated by the 
regulatory citations provided by the petitioner in support of its 
contention, FDA's focus is on human health effects. In the particular 
case of zinc oxide, EPA's decision to deny the petition to delist is 
based on the environmental impacts of the chemical.

V. References

    (1) Lloyd, T.B., Zinc Compounds. In: Kirk-Othmer Encyclopedia of 
Chemical Technology, 3rd ed., Vol. 24, pp. 851863, New York (1984).
    (2) Merck and Co., The Merck Index, 11th ed., p. 1599 (1989).
    (3) Weast, R.C., ed., Handbook of Chemistry and Physics, 70th ed., 
CRC Press, Inc., p. B-144, Boca Raton (1989).
    (4) Dean, J.A., ed., Lange's Handbook of Chemistry, 13th ed., 
McGraw-Hill, pp. 4-131, New York (1985).
    (5) ATSDR, Toxicological profile for zinc. US Department of Health 
and Human Services, Public Health Service, Agency for Toxic Substances 
and Disease Registry, p. 109 (1994).
    (6) Aylett, B.J., Group IIB. In: Comprehensive Inorganic Chemistry, 
Bailar, H.J., Jr., Emeleus, R.N., Trotman-Dickenson, A.F., eds., 
Pergamon Press, p. 217, Oxford (1973).
    (7) Durrant, P.J. and Durrant, B., Introduction to Advanced 
Inorganic Chemistry, 2nd ed., John Wiley Sons, p. 395, New York (1970).
    (8) Linke, W.F., Solubilities of Inorganic and Metal-Organic 
Compounds, D. Van Nostrand Co., Inc., Princeton (1958).
    (9) Pourbaix, M., Atlas of Electrochemical Equilibria in Aqueous 
Solutions, National Association of Corrosion Engineers, pp. 406-413, 
Houston (1974).
    (10) Cotton, F.A. and Wilkenson, G., Advanced Inorganic Chemistry, 
A Comprehensive Text, 2nd ed., John Wiley Sons, pp. 604-608, New York 
(1986).
    (11) Pauling, L., General Chemistry, 3rd ed., Freeman and Company, 
San Francisco (1970).
    (12) Bodek, I., Environmental Inorganic Chemistry, Properties, 
Processes, and Estimation Methods, Pergamon Press, pp. 7.15/1-7.15/11, 
New York (1988).
    (13) USEPA/OPPT, Smrchek, Jerry C., Petition to Delist Zinc 
Sulfide-Hazard Review dated March 28, 1990.
    (14) USEPA/OPPT, Meyn, Ossi, Petition to Delist Zinc Oxide dated 
June 21, 1995.

VI. Administrative Record

    The record supporting this decision is contained in docket number 
OPPTS-400098. All documents, including an index of the docket, are 
available to the public in the TSCA Nonconfidential Information Center 
(NCIC), also known as the Public Docket Office, from noon to 4 p.m., 
Monday through Friday, excluding legal holidays. The TSCA NCIC is 
located at EPA Headquarters, Rm. NE-B607, 401 M St., SW., Washington, 
DC 20460.

List of Subjects in 40 CFR Part 372

    Environmental protection, Chemicals, Community right-to-know, 
Reporting and recordkeeping requirements, and Toxic chemicals.

    Dated: September 1, 1995.
Lynn R. Goldman,
Assistant Administrator, Office of Prevention, Pesticides and Toxic 
Substances.

[FR Doc. 95-22618 Filed 9-11-95; 8:45 am]
BILLING CODE 6560-50-F