Soluble Silicates - ACS Publications - American Chemical Society

3 Current Regulatory Status of Soluble Silicates J. G. BLUMBERG and W. L. SCHLEYER

Downloaded by GEORGETOWN UNIV on June 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

The PQ Corporation, Research and Development Center, Lafayette Hill, PA 19444

Federal agency promulgations authorizing or affect ing the soluble silicates are compiled. Their safety has been extensively reviewed. For caution ary labeling, i t is industry practice to group com mercial soluble silicate products into three hazard classes. Occupational exposure limits vary simil arly with alkalinity. The warning language for con sumer products, notably household detergents, may be affected by the type and quantity of their sol uble silicate content. Soluble silicates have both GRAS and additive regulation status for food uses. As inert ingredients, sodium silicate and metasili cate are exempt from the requirement of a pesticide residue tolerance. They are also classed as active pesticidal ingredients and thereby exposed to inap propriate generic regulation. Only highly alkaline forms of sodium silicate are regulated as hazardous materials for transportation purposes and, when dis carded, are classified as hazardous waste. Except to that extent, soluble silicates are not hazardous substances under spill regulations. The proposed Preliminary Assessment Information Rule under TOSCA included soluble silicates. For inventory reporting purposes, currently available sodium silicates are three "chemical substances." The environmental -regulatory profile of soluble silicates provides incentive for their preference over more hazardous and more highly regulated alternate materials. Safety Reviews High tonnage production combined with consumer r e l a t e d uses i n food and detergents have occasioned extensive reviews o f the long-range s a f e t y o f sodium s i l i c a t e . Both i n the environment and i n the body, i t degrades to s i l i c a which i s i n d i s t i n g u i s h 0097-6156/82/0194-0031$06.00/0 ©

1 9 8 2 A m e r i c a n C h e m i c a l Society

Falcone; Soluble Silicates ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


32

SOLUBLE

SILICATES

able from n a t u r a l l y o c c u r r i n g forms. Furthermore, i t has a long h i s t o r y o f p r o d u c t i o n and safe use. Therefore, i t i s not s u r p r i s i n g that l i t t l e need has been seen to confirm the absence of c h r o n i c h e a l t h e f f e c t s by thorough l a b o r a t o r y s t u d i e s . The recent commercialization o f laundry detergent c o n t a i n i n g z e o l i t e A has, i n e f f e c t , added to the a v a i l a b l e i n f o r m a t i o n , because sodium s i l i c a t e forms when z e o l i t e A breaks down (\). A comprehensive review o f sodium and potassium s i l i c a t e was conducted by the Select Committee on GRAS Substances o f the L i f e Sciences Research O f f i c e , F e d e r a t i o n o f American S o c i e t i e s f o r Experimental B i o l o g y (FASEB) f o r the Food and Drug Administration. I t was concluded that "there i s no evidence i n the a v a i l a b l e information on ... potassium [and] sodium s i l i c a t e that demonstrates or suggests reasonable grounds to suspect a hazard to the p u b l i c when they are used at l e v e l s that are current or that might reasonably be expected i n the future" ( 2 ) . The e v a l u a t i o n was based i n part on a s c i e n t i f i c l i t e r a t u r e review with 544 r e f e r e n c e s , sponsored by the Food and Drug A d m i n i s t r a t i o n (3) . The I n t e r n a t i o n a l J o i n t Commission (U.S.-Canada) under the Great Lakes Water Q u a l i t y Agreement undertook a s a f e t y review o f detergent b u i l d e r s which encompassed both human h e a l t h and environmental aspects. The Task Force on the Health E f f e c t s o f Non-NTA Detergent B u i l d e r s o f the IJC*s Great Lakes Science Advisory Board concluded that "the use o f sodium s i l i c a t e i n detergents poses no hazard to man" (4·). A separate Task Force on the E c o l o g i c a l E f f e c t s o f Phosphate Replacements has not yet issued a r e p o r t , but i t i s understood to have concluded that there i s no cause f o r concern ( 5 ) . Sodium and potassium s i l i c a t e are the s o l u b l e s i l i c a t e s o f commercial importance. For potassium s i l i c a t e , not n e a r l y as extensive data from the l a b o r a t o r y or from human experience are a v a i l a b l e . The assumption of i t s s i m i l a r i t y to sodium s i l i c a t e i n h e a l t h and environmental e f f e c t s appears to be v a l i d , f o r an equivalent mole r a t i o o f S 1 O 2 to a l k a l i metal oxide. Although s o l u b l e s i l i c a t e s are produced from quartz sand, they do not c o n t a i n d e t e c t a b l e amounts o f c r y s t a l l i n e s i l i c a . A l l evidence p o i n t s to the moderate to strong a l k a l i n i t y o f s o l u b l e s i l i c a t e s as the sole source o f a p o t e n t i a l hazard to human h e a l t h or environment. The r e g u l a t o r y c o n t r o l s c u r r e n t l y i n e f f e c t stem e i t h e r from t h i s acute hazard or from t h e i r use i n regulated a p p l i c a t i o n s . The e n t i r e r e g u l a t o r y spectrum i s d e s c r i b e d here, i n s o f a r as i t would concern processors or users o f s o l u b l e s i l i c a t e s i n the United S t a t e s . Workplace Although chemical hazard communication has been o f concern



3.

BLUMBERG

A N D SCHLEYER

Current

Regulatory

Status

33

to the Occupational Safety and Health A d m i n i s t r a t i o n o f the U.S. Department o f Labor (OSHA) since i t s i n c e p t i o n i n 1972, c a u t i o n a r y l a b e l i n g o f i n d u s t r i a l chemicals remains to t h i s day a v o l u n t a r y i n d u s t r i a l p r a c t i c e . The most widely used system i s set f o r t h i n ANSI Standard Z129.1-1976 ( 6 ) . The standard d e f i n e s hazard c l a s s e s and s p e c i f i e s the a p p l i c a b l e l a b e l language. By these c r i t e r i a , the s i l i c a t e s c o n s t i t u t e three d i f f e r e n t hazard c l a s s e s because r i s i n g a l k a l i n i t y increases the s e v e r i t y o f the hazard. Since s i l i c a t e s are good b u f f e r s , t h e i r Si02/Na20 r a t i o i s a f a r more important determinant o f the degree o f a l k a l i n i t y than i s t h e i r c o n c e n t r a t i o n l e v e l . Commercial sodium s i l i c a t e l i q u i d s o f 2.0 r a t i o or g r e a t e r and d r y sodium s i l i c a t e o f at l e a s t 2.4 r a t i o c o n s t i t u t e the l e a s t hazardous group: they cause eye and s k i n i r r i t a t i o n . Sodium m e t a s i l i c a t e , sodium o r t h o s i l i c a t e and 1.6 r a t i o sodium s i l i c a t e l i q u i d s f a l l i n t o the c l a s s o f highest hazard: they are c o r r o s i v e , i . e . , cause eye and s k i n burns. The intermediate hazard c l a s s c o n s i s t s o f d r y s i l i c a t e s and l i q u i d s between the other two c l a s s e s i n r a t i o , which are considered c o r r o s i v e t o the eye but not to the s k i n . T y p i c a l i n d u s t r i a l l a b e l s f o r a r e p r e s e n t a t i v e sodium s i l i c a t e product from each hazard c l a s s are shown i n F i g s . 1-3. Since commercial potassium s i l i c a t e products range i n S 1 O 2 / K 2 O mole r a t i o only from approximately 2.5 t o 3.9, a l l f a l l i n t o the lowest hazard c l a s s : they are eye and s k i n irritants. Although OSHA Form 20 or one approved as e s s e n t i a l l y s i m i l a r i s mandatory only i n the maritime trades ( 7 ) , i t has become customary throughout the chemical i n d u s t r y to o b t a i n or prepare a m a t e r i a l s a f e t y data sheet before a new chemical enters a workplace. For products i n the same i n d u s t r i a l hazard c l a s s the information provided on the m a t e r i a l s a f e t y data sheet i s the same, except as modified by d i f f e r e n c e s i n p h y s i c a l p r o p e r t i e s . For example, the s p i l l removal i n s t r u c t i o n s f o r l i q u i d s are d i f f e r e n t from those f o r s o l i d s . F i g s . 4a and 4b show a m a t e r i a l s a f e t y data sheet f o r a dry, powdered sodium s i l i c a t e i n the lowest hazard c l a s s . Word processing equipment i s v e r y u s e f u l f o r m a i n t a i n i n g and p r o v i d i n g t h i s i n f o r m a t i o n , as well as f o r r e c o r d i n g and r e t r i e v i n g those who r e c e i v e d i t . I t may be noted that the sheet c o n t a i n s more than o c c u p a t i o n a l s a f e t y data. I t i n c l u d e s s p i l l response and TOSCA data as w e l l . It i s evolving into a s a f e t y and r e g u l a t o r y data sheet. There are no s p e c i f i c OSHA exposure standards f o r sodium or potassium s i l i c a t e . Depending on r a t e o f s o l u t i o n and degree o f a l k a l i n i t y o f a i r b o r n e m a t e r i a l s , a prudent i n d u s t r i a l exposure standard could range from the p e r m i s s i b l e exposure l i m i t (PEL) for i n e r t or nuisance p a r t i c u l a t e s up t o n e a r l y the PEL f o r sodium hydroxide.


SOLUBLE

34

WARNING! CAUSES IRRITATION


Avoid contact with eyes, skin, and clothing. Wash thoroughly after handling. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Call a physician. Flush skin with water. SPILLAGE: Mop up and flush to sewer with plenty of water. FOR INDUSTRIAL USE ONLY COVER WHEN NOT IN USE PROTECT FROM FREEZING Figure 1.

Sodium silicate cautionary label, least hazardous class.

DANGER! CAUSES EYE AND SKIN BURNS Do not get in eyes, on skin, on clothing. Avoid breathing mist. Keep container closed. Use with adequate ventilation. Wash thoroughly after handling. Do not take internally. When handling, wear goggles or face shield. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes or skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Call a physician. ANTIDOTE: If swallowed, do NOT induce vomiting. Give large quantities of water. Give at least one ounce of vinegar in an equal amount of water. Never give anything by mouth to an unconscious person. Call a physician. SPILLAGE: Mop up and flush to sewer with plenty of water. Figure 2.

Sodium silicate cautionary label, most hazardous class.


SILICATES


BLUMBERG AND SCHLEYER

Current

Regulatory

Status

DANGER! CAUSES EYE BURNS, CAUSES SKIN IRRITATION Do not get in eyes, on skin, on clothing. Avoid breathing mist. Keep container closed. Use with adequate ventilation. Wash thoroughly after handling. Do not take internally. When handling, wear goggles or face shield. Wash contaminated clothing before re-use. FIRST AID: In case of contact, immediately flush eyes with plenty of water for at least 15 miniutes. Call a physician. Flush skin with water. ANTIDOTE: If swallowed, do NOT induce vomiting. Give large quantities of water. Give at least one ounce of vinegar in an equal amount of water. Never give anything by mouth to an unconscious person. Call a physician. SPILLAGE: Mop up and flush to sewer with plenty of water. Figure 3.

Sodium silicate cautionary

label, intermediate

hazardous

class.


SOLUBLE

36

SECTION

1.

IDENTIFICATION

MANUFACTURER: ADDRESS:

PQ

OF

SALES N A M E :

CORPORATION

BRITESIL C-24

CHEMICAL NAME:


No.:

HAZARD

DOT

SHIPPING N A M E : N . A . SECTION

APPEARANCE Odorless.

PHYSICAL

& ODOR:

SPECIFIC G R A V I T Y

DATA

(liquids o n l y ) : N . A . Complete.

P R E S S U R E ( m m H g at ° F , nonaqueous liquids o n l y ) : N . A . RATE

CONTENT

BOILING POINT VAPOR

1344-09-8

A q u a m a r i n e glassy l u m p s , white granules, o r white powder.

IN WATER:

EVAPORATION SOLIDS

293-7200

CLASS: N.A.

2.

SOLUBILITY

(215)

sodium silicate

R

Silicic a c i d , s o d i u m salt*

CAS REGISTRY

DOT

VAPOR

PRODUCT

11 E X E C U T I V E M A L L , P . O . B O X 8 4 0 , V A L L E Y F O R G E , P A 19482

EMERGENCY TELEPHONE NUMBER:

TOSCA

SILICATES

( B u t y l acetate = 100, nonaqueous liquids o n l y ) : N . A .

(solutions dispersions, o r pastes only) : N . A .

( ° F , nonaqueous l i q u i d s o n l y ) : N . A .

DENSITY

(nonaqueous liquids o n l y ) : N . A .

p H (aqueous liquids only) : N . A .

SECTION

3.

F L A S H POINT

FIRE A N D EXPLOSION HAZARD

DATA

(°F): N . A .

F L A M M A B L E L I M I T S (vapor i n a i r , V o l . % ) : N . A . FIRE EXTINGUISHING

MEDIA:

SPECIAL FIRE FIGHTING

N.A.

PROCEDURES:

N.A.

UNUSUAL FIRE A N D EXPLOSION HAZARDS:

S E C T I O N 4. STABILITY:

REACTIVITY

None

DATA

Stable

CONDITIONS

TO AVOID:

INCOMPATIBILITY HAZARDOUS

N.A.

(Materials to A v o i d ) : N . A .

DECOMPOSITION

PRODUCTS:

None

N . A . = N o t Applicable * Includes other h a z a r d classes, to w h i c h different safety data sheets apply. Figure 4a.

Material safety data sheet; high ratio powders, side 1.


3.

Current

BLUMBERG A N DSCHLEYER

S E C T I O N 5.

SPILL OR L E A K

Regulatory

37

Status

PROCEDURES

S P I L L A G E : Sweep, scoop, o r v a c u u m discharged material. Observe environmental protection regulations.

F l u s h residue w i t h water.

W A S T E D I S P O S A L M E T H O D : N e u t r a l i z e with dilute acid and landfill solids according to l o c a l , state, a n d federal regulations. F l u s h n e u t r a l l i q u i d to sewer with plenty of water.

S E C T I O N 6.


EYE

HEALTH HAZARD

CONTACT

DATA

Causes irritation.

SKIN CONTACT: INHALATION :

Causes irritation.

D u s t m a y irritate respiratory tract.

F I R S T A I D P R O C E D U R E S : I n case of contact, immediately flush eyes w i t h plenty of water for at least 15 minutes. C a l l a physician. F l u s h s k i n w i t h water. M E D I C A L EXAMINATIONS: N.A.

S E C T I O N 7. RESPIRATORY occurs. GLOVES: EYE

SPECIAL PROTECTION PROTECTION:

Use N I O S H

INFORMATION approved

dust respirator where

dust

R u b b e r where contact l i k e l y .

PROTECTION :

C h e m i c a l goggles a n d / o r face shield.

OTHER PROTECTIVE EQUIPMENT: w i t h i n direct access.

Safety shower a n d eyewash fountain should be

P E R S O N A L H Y G I E N E : A v o i d contact with eyes, s k i n , and clothing. W a s h thoroughly after h a n d l i n g . W a s h contaminated clothing before re-use. ENGINEERING CONTROL:

S E C T I O N 8.

N.A.

SUBSTANCES FOR WHICH STANDARDS

SINGLE CHEMICAL SUBSTANCE: Percent: N . A . O S H A Exposure L i m i t : EXPOSURE ANALYSIS

S E C T I O N 9.

N.A.

COMPONENTS: Percent: N . A .

N.A.

O S H A Exposure L i m i t :

METHODS:

SOURCE OF

W a l t e r L . Schleyer

N.A.

HAVE BEEN

N.A.

N.A.

INFORMATION

G o v ' t & Industry R e l a t i o n s M a n a g e r

Date: 7 / 1 7 / 7 9

N . A . = N o t Applicable Figure 4b.

Material

safety data sheet; high ratio powders, side 2.


SET

SOLUBLE

38

SILICATES


Consumer Products Years ago, sodium m e t a s i l i c a t e was the only r e a d i l y s o l u b l e sodium s i l i c a t e a v a i l a b l e i n dry form. I t was used i n dry blended home laundry detergents and i n automatic dishwasher detergents. When low-phosphate and phosphate-free detergents f i r s t came on the market, some of them c a r r i e d an increased m e t a s i l i c a t e content, and concern arose about t h e i r safety i n the home. Although sodium m e t a s i l i c a t e i s c o r r o s i v e to b i o l o g i c a l t i s s u e , t h i s i s not n e c e s s a r i l y true of detergents i n which i t i s an i n g r e d i e n t . Among determining f a c t o r s are the amount used, i t s p a r t i c l e s i z i n g , the processing method, and the modifying e f f e c t of other i n g r e d i e n t s . The Consumer Product Safety Commission has recognized t h i s . It has e s t a b l i s h e d l a b e l i n g c r i t e r i a based on the r e s u l t s of b i o l o g i c a l t e s t i n g , as s p e c i f i e d under the Federal Hazardous Substances Act. I f the product contains 15% sodium m e t a s i l i c a t e or more and i f no animal t e s t data to the c o n t r a r y are a v a i l a b l e , i n s p e c t o r s are i n s t r u c t e d to r e q u i r e "DANGER! MAY CAUSE BURNS" on the l a b e l . Less severe warning language i s s p e c i f i e d f o r lower m e t a s i l i c a t e content and l e s s strongly a l k a l i n e types of s i l i c a t e i n g r e d i e n t s ( 8 ) . Both the animal t e s t methods (9) and the c a u t i o n l a b e l language are c u r r e n t l y under review w i t h i n the agency and i t s T o x i c o l o g i c a l Advisory Board. Readily soluble but l e s s s t r o n g l y a l k a l i n e hydrous sodium p o l y s i l i c a t e m a t e r i a l s have long since been a v a i l a b l e as i n g r e d i e n t s of dry blended detergents. Unlike sodium m e t a s i l i c a t e , these f a l l i n t o the intermediate or lowest s i l i c a t e l a b e l hazard c l a s s , depending on t h e i r Si02/Na2Û ratio. The household hazard i s correspondingly reduced. The bulk of household detergents i s spray d r i e d from s l u r r i e s which comprise a sodium s i l i c a t e s o l u t i o n . The f i n i s h e d product then c o n s i s t s of homogeneous beads, and not of d i s c r e t e p a r t i c l e s of i t s components, u s u a l l y r e s u l t i n g i n l e s s e r hazard characteristics. Food Uses We begin with a g l o s s a r y o f the terms by which the r e g u l a t o r y status of food i n g r e d i e n t s i s d e f i n e d . To be used i n food, a chemical substance must be e i t h e r a "food a d d i t i v e " or "Generally Recognized As Safe (GRAS)" or " p r i o r sanctioned." Each food a d d i t i v e and i t s uses i s described by an FDA r e g u l a t i o n (10), issued i n response to a food a d d i t i v e p e t i t i o n which was supported by f u l l r e p o r t s of i n v e s t i g a t i o n s i n t o i t s safety. A GRAS substance i s " g e n e r a l l y recognized, among experts q u a l i f i e d by s c i e n t i f i c t r a i n i n g and experience to evaluate i t s safety, as having been adequately shown through s c i e n t i f i c


3.

BLUMBERG A N D SCHLEYER

Current

Regulatory

Status

procedures to be safe under the c o n d i t i o n s o f i t s intended use"(ll). A~" prior sanctioned" substance i s one which i s used i n accordance with a s a n c t i o n or approval granted p r i o r t o enactment o f the 1958 Food A d d i t i v e Amendments to the F e d e r a l Food, Drug and Cosmetic Act (11). Today the s c i e n t i f i c evidence r e q u i r e d to show GRAS s t a t u s i s equal i n extent t o the documentation which must be submitted i n support o f a food a d d i t i v e p e t i t i o n (12). However, there i s a grandfather c l a u s e i n the case o f a substance used i n food p r i o r to January 1, 1958: s a f e t y may be shown e i t h e r through s c i e n t i f i c procedures or through experience based on common use i n food (11). In 1973 FDA embarked on i t s GRAS review process, under which chemicals " G e n e r a l l y Recognized As Safe" are being reexamined for s a f e t y . Those affirmed w i l l be c o d i f i e d , that i s , l i s t e d i n T i t l e 21 o f the Code o f F e d e r a l Regulations (13). Those not affirmed w i l l no longer be considered GRAS by FDA, so that an approved food a d d i t i v e p e t i t i o n w i l l be r e q u i r e d f o r t h e i r use i n food (lb). Examples o f substances which are regarded as GRAS already appear i n the Code (15), but many more are p r e s e n t l y unpublished. Unpublished GRAS s t a t u s can a r i s e from an FDA o p i n i o n l e t t e r i n response to an i n q u i r y or from a determination by i n d u s t r y that a substance i s GRAS. FDA bears the burden o f proof that such a substance i s not GRAS (16). S p e c i f i c a t i o n s f o r food chemicals are to be found i n the Food Chemicals Codex (17). T h i s compendium i s prepared by the Food and N u t r i t i o n Board o f the N a t i o n a l Research C o u n c i l . I t contains monographs o f many food chemicals and i s recognized by the Food and Drug A d m i n i s t r a t i o n as d e f i n i n g t h e i r "appropriate food grade" w i t h i n the meaning o f FDA r e g u l a t i o n s (12,18). The use o f sodium s i l i c a t e for p r e s e r v i n g eggs apparently escaped government s c r u t i n y by timely obsolescence. The use o f sodium s i l i c a t e as a c o r r o s i o n i n h i b i t o r i n d r i n k i n g water was passed on a f f i r m a t i v e l y by the Surgeon General o f the P u b l i c Health Service i n 1937 (19). In the e a r l y 1960s FDA issued a s e r i e s o f o p i n i o n l e t t e r s s t a t i n g that sodium s i l i c a t e up t o 100 ppm would be " g e n e r a l l y recognized as s a f e " i n canned d r i n k i n g water as w e l l as i n other potable water systems ( 2 ) . L a t e r i t s use was mandated by a f e d e r a l m i l i t a r y s p e c i f i c a t i o n f o r canned emergency d r i n k i n g water (20), since sodium s i l i c a t e remained the only a d d i t i v e acceptable t o the Food and Drug A d m i n i s t r a t i o n . Because o f t h i s unpublished GRAS s t a t u s , sodium and potassium s i l i c a t e s were included i n the GRAS Review process. In 1979 the S e l e c t Committee on GRAS Substances issued an a f f i r m a t i v e report (2) [see Safety Reviews above] and i n d u s t r y submitted proposed food grade s p e c i f i c a t i o n s , but the r e g u l a t o r y process has not yet reached F e d e r a l R e g i s t e r p u b l i c a t i o n . Sodium and potassium s i l i c a t e and sodium m e t a s i l i c a t e monographs n


39



40

SOLUBLE

SILICATES

have a l s o been proposed f o r i n c l u s i o n i n the Food Chemicals Codex. Sodium s i l i c a t e has published GRAS s t a t u s as a substance m i g r a t i n g t o food from paper and paperboard products used i n food packaging (21), and from cotton and cotton f a b r i c s used i n dry food packaging (22). These are i n d i r e c t food uses. Sodium s i l i c a t e has r e g u l a t i o n status as a b o i l e r water a d d i t i v e i n the p r e p a r a t i o n o f steam that w i l l contact food (23); i n z i n c - s i l i c o n d i o x i d e matrix coatings (24); and as a c o n s t i t u e n t o f cellophane used f o r packaging food TÏ5). Sodium m e t a s i l i c a t e , although merely one species o f sodium s i l i c a t e , has a r e g u l a t o r y i d e n t i t y o f i t s own, perhaps because of i t s c r y s t a l l i n e form and s t o i c h i o m e t r i c nature. I t has unpublished GRAS status f o r f r u i t and vegetable washing (26,29), as a r e f i n i n g agent f o r e d i b l e rendered f a t s (26); as a p e e l i n g s o l u t i o n f o r peaches (27); and as a component o f s a n i t i z i n g s o l u t i o n s intended f o r use on food contact surfaces (29)· I t entered GRAS review as a separate e n t i t y . The S e l e c t Committee, i n a 1977 t e n t a t i v e r e p o r t (26), d i d not pass on i t s s a f e t y , f e e l i n g i t had i n s u f f i c i e n t information. FDA then commissioned a l i t e r a t u r e review (28), and, i n a 1981 f i n a l r e p o r t , the S e l e c t Committee recommended Class I s t a t u s f o r sodium m e t a s i l i c a t e t o the FDA. This was expressed i n analogy t o the statement on sodium and potassium s i l i c a t e s , quoted on page 2 (29). C o d i f i c a t i o n , the f i n a l step i n the GRAS a f f i r m a t i o n process, could be another two years away. Sodium m e t a s i l i c a t e has food a d d i t i v e r e g u l a t i o n status as b o i l e r water a d d i t i v e i n the p r e p a r a t i o n o f steam that w i l l contact food (23). In a d d i t i o n i t i s b e l i e v e d to be " p r i o r sanctioned" under the Meat I n s p e c t i o n A c t f o r hog s c a l d i n g and t r i p e denuding. The U.S. Department o f A g r i c u l t u r e * s Food Safety and Q u a l i t y Service has o r i g i n a l j u r i s d i c t i o n under the Federal Meat Inspection Act and the P o u l t r y Products Inspection A c t . I t has approved sodium m e t a s i l i c a t e as c o o l i n g and r e t o r t water treatment agent, as t r i p e denuding agent, and as hog s c a l d agent (30) . Sodium ortho and sesqui s i l i c a t e s are s i m i l a r l y approved. Based on USDA s and FDA s r e g u l a t o r y schemes, the Meat and P o u l t r y I n s p e c t i o n Program, Animal and Plant Health Inspection Service o f the U.S. Department o f A g r i c u l a t u r e has approved s p e c i f i c sodium s i l i c a t e and/or sodium m e t a s i l i c a t e products as general c l e a n i n g agents f o r food contact s u r f a c e s , f o r t r e a t i n g b o i l e r and c o o l i n g system water, as water c o n d i t i o n e r , as wetting agent f o r use i n p o u l t r y s c a l d v a t s , i n hog s c a l d i n g and t r i p e denuding, and t o wash f r u i t and vegetables that are t o become i n g r e d i e n t s o f p o u l t r y , meat, r a b b i t and egg products (31) . The d i f f e r e n c e i n r e g u l a t o r y s t r u c t u r e i s that FDA and USDA r u l e s set generic standards, whereas the Méat and P o u l t r y Inspection Program must authorize every s i n g l e commercial product o f each s u p p l i e r , i n c l u d i n g p r o p r i e t a r y mixtures, before i t s admission t o a f e d e r a l l y inspected food packing p l a n t . f

9



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41

Recently the Safe D r i n k i n g Water Act t r a n s f e r r e d j u r i s d i c t i o n f o r potable water, other than water used i n food and b o t t l e d water, from the FDA to the Environmental P r o t e c t i o n Agency. EPA i s planning a c o n t r o l program f o r water treatment chemicals and, i n a memorandum o f agreement with FDA, announced (32) that i t had contracted with the N a t i o n a l Academy of Sciences to develop a compendium of approved substances and s p e c i f i c a t i o n s , comparable to the Food Chemicals Codex. No chemicals have so f a r become known to have been s e l e c t e d f o r i n c l u s i o n . H i s t o r i c a l l y , the use of sodium s i l i c a t e , and of a c t i v a t e d s i l i c a s o l prepared from sodium s i l i c a t e , f o r t r e a t i n g p u b l i c water s u p p l i e s has been authorized by p u b l i c h e a l t h agencies on the s t a t e l e v e l . The amount of s o l u b l e s i l i c a t e s consumed i n regulated food uses i s small compared to the tonnage consumed i n the c l e a n i n g of food contact s u r f a c e s . Since i t i s considered that there i s no residue of c l e a n i n g agents when the surfaces have been r i n s e d with potable water, the detergent uses are unregulated. Recognition of the s a f e t y of the s o l u b l e s i l i c a t e s i n food i s considered important because of the e v e n t u a l i t y that u t e n s i l c l e a n i n g agents would some day be regulated as chemical food ingredients. Pesticide

Formulations

Sodium s i l i c a t e and sodium m e t a s i l i c a t e are exempt from the requirement of a residue t o l e r a n c e i n p e s t i c i d e formulations a p p l i e d to growing crops or to raw a g r i c u l t u r a l commodities a f t e r harvest (33). The detergency b u i l d e r and b u f f e r i n g c h a r a c t e r i s t i c s of sodium s i l i c a t e and m e t a s i l i c a t e have l e d to t h e i r i n c l u s i o n i n about 480 EPA-registered detergent s a n i t i z e r products. Relying apparently on an h i s t o r i c a l master l i s t of substances f o r which p e s t i c i d a l a c t i v i t y had ever been claimed by any a p p l i c a n t f o r a p e s t i c i d e r e g i s t r a t i o n , EPA regards the s i l i c a t e s as a c t i v e i n g r e d i e n t s whenever they are part of a p e s t i c i d e formulation. In most i f not a l l such formulations, s i l i c a t e performs as an adjuvant and has no a n t i m i c r o b i a l a c t i v i t y o f i t s own at use c o n c e n t r a t i o n . Therefore i t does not meet FIFRA (34) d e f i n i t i o n of a p e s t i c i d e . With p e s t i c i d e r e g u l a t i o n tightened i n recent years, the presence of s o l u b l e s i l i c a t e s on EPA*s p e s t i c i d e a c t i v e s master l i s t threatens i t s i n d i s c r i m i n a t e r e g u l a t i o n , along with many other common i n d u s t r i a l chemicals of low hazard p o t e n t i a l . A c o n t r o l program (35) d i r e c t e d at t e c h n i c a l a c t i v e s not h i t h e r t o subject to p e s t i c i d e r e g u l a t i o n , such as kepone, should not be purposely or i n a d v e r t e n t l y extended to multi-purpose commodity chemicals which are already regulated under the Toxic Substances C o n t r o l Act (TOSCA). Examples of i n a p p r o p r i a t e uses of the


42

SOLUBLE

SILICATES

e n t i r e l i s t f o r r e g u l a t o r y purposes are: a proposed scheme f o r recordkeeping, r e p o r t i n g and p e s t i c i d e manufacturing establishment r e g i s t r a t i o n (36); and a p o s s i b l e generic OSHA standard f o r occupational exposure t o p e s t i c i d e s during manufacture and formulation (37). I t has been reported i n newsletters that EPA plans t o remove at l e a s t 114 chemicals, i n c l u d i n g the s o l u b l e s i l i c a t e s , from a c t i v e p e s t i c i d a l i n g r e d i e n t s t a t u s , but no o f f i c i a l a c t i o n has as yet been taken.


Transportation Sodium s i l i c a t e l i q u i d s o f 1.6 Si02/Na 0 r a t i o or l e s s and sodium o r t h o s i l i c a t e meet the c r i t e r i a (38) f o r r e g u l a t i o n as c o r r o s i v e m a t e r i a l s f o r purposes o f t r a n s p o r a t i o n . As n e i t h e r substance i s l i s t e d s p e c i f i c a l l y i n the DOT Hazardous M a t e r i a l s Table (39), the proper shipping names are, r e s p e c t i v e l y , a l k a l i n e ( c o r r o s i v e ) l i q u i d , n.o.s. and c o r r o s i v e s o l i d n.o.s. DOT r e g u l a t i o n s p r e s c r i b e the proper manner o f packaging (38), preparing shipping papers, marking, l a b e l i n g (with the diamond-shaped l a b e l bearing the " c o r r o s i v e " legend and symbols), and v e h i c l e p l a c a r d i n g (40). "Limited q u a n t i t i e s " i n surface t r a n s p o r t a t i o n are exempt from many o f these requirements (41). More s t r i n g e n t r u l e s apply to t r a n s p o r t a t i o n by a i r (427, where a f u r t h e r d i s t i n c t i o n as t o net quantity l i m i t i n a s i n g l e package i s made between passenger-carrying and cargo-only a i r c r a f t . Only the DOT r u l e s which are generic t o c o r r o s i v e m a t e r i a l s apply t o those s o l u b l e s i l i c a t e s o f very high degree o f a l k a l i n i t y . Hence, they are mentioned as being a p p l i c a b l e , but not explained f u r t h e r . As discussed i n the next s e c t i o n , c e r t a i n sodium s i l i c a t e l i q u i d s which do not meet DOT c r i t e r i a f o r a c o r r o s i v e l i q u i d are hazardous waste under RCRA when discarded. These are DOT-regulated as ORM-E (43). S i m i l a r l y , the d r y blends which are i d e n t i f i e d i n the next S e c t i o n as EPA hazardous substances because o f t h e i r sodium hydroxide content are DOT-regulated as ORM-E, i f they c o n t a i n the r e p o r t a b l e quantity o f 1,000 l b . NaOH i n a s i n g l e package or bulk c o n t a i n e r . 2

P o l l u t i o n and Waste C o n t r o l The e f f l u e n t l i m i t a t i o n g u i d e l i n e s governing users o f s o l u b l e s i l i c a t e s are determined by t h e i r standard i n d u s t r y c l a s s i f i c a t i o n (SIC Number). I t may be noted that the sodium s i l i c a t e subcategory o f the Inorganic Chemicals Manufacturing Industry has been excluded from f u r t h e r rulemaking under the National Resources Defense Council v . C o s t l e consent decree because o f the absence or v i r t u a l absence o f 65 t o x i c p o l l u t a n t s from the i n d u s t r y s e f f l u e n t s (44). Because o f high temperature manufacturing processes, aqueous media and high i n s o l u b i l i t y o f 1



3.


Current

Regulatory

Status

43

the s i l i c a t e s of most metals, the commercial s o l u b l e s i l i c a t e s are g e n e r a l l y low i n both organic and i n o r g a n i c i m p u r i t i e s . T y p i c a l values are shown i n Table 1.(45). T h e i r range represents eleven producing p o i n t s which are l o c a t e d throughout the United States and employ d i f f e r e n t manufacturing processes. The s o l u b l e s i l i c a t e s are not designated as hazardous substances under Section 311 o f the F e d e r a l Water P o l l u t i o n ' C o n t r o l Act, r e l a t i n g to discharges or s p i l l s i n t o navigable waters (46). However, some commercial sodium o r t h o s i l i c a t e products are a c t u a l l y p h y s i c a l blends of sodium hydroxide and sodium m e t a s i l i c a t e p a r t i c l e s . Such mixtures are EPA hazardous substances by v i r t u e of t h e i r sodium hydroxide content, and t h e i r r e p a r t a b l e q u a n t i t y i s the equivalent of 1,000 l b s o f sodium hydroxide (47). In terms of the Resource Conservation and Recovery Act of 1976 (RCRA) sodium s i l i c a t e i s not among c e r t a i n chemicals which have been designated as rendering a waste hazardous (48). However, a waste i s a l s o c l a s s i f i e d as hazardous i f i t e x h i b i t s c e r t a i n c h a r a c t e r i s t i c s (49). One of these i s c o r r o s i v i t y . On the a l k a l i n e s i d e , c o r r o s i v i t y i s defined by a pH equal to or greater than 12.5, provided the waste i s aqueous (50). We have measured the pH o f v a r i o u s sodium s i l i c a t e s o l u t i o n s by EPA*s reference method. According to our r e s u l t s , sodium s i l i c a t e s o l u t i o n s have a pH of 12.5 or g r e a t e r when a. r e g a r d l e s s of c o n c e n t r a t i o n , the Si02/Na20 weight r a t i o i s l e s s than 2.0; and b. the Si02/Na20 r a t i o i s equal to 2.0 and the s o l i d s c o n c e n t r a t i o n i s approximately 44% or greater. Below that c o n c e n t r a t i o n and at a l l concentrations above 2.0 r a t i o the pH remained below 12.5. On November 17, 1980, EPA proposed t o grant a permit-by-rule to operators o f "elementary n e u t r a l i z a t i o n u n i t s , " d e f i n e d as devices that are used f o r n e u t r a l i z i n g wastes which are hazardous wastes only because they e x h i b i t the c o r r o s i v i t y c h a r a c t e r i s t i c s . Pending completion o f t h i s rulemaking, EPA has suspended i t s permit requirements f o r e l i g i b l e operators. As a r e s u l t , operators of "elementary n e u t r a l i z a t i o n u n i t s " no longer need RCRA permits on a case-by-case b a s i s , only a r e g i s t r a t i o n number (51). When sodium s i l i c a t e s o l u t i o n s at or above pH 12.5 become wastes, they are "hazardous wastes only because they e x h i b i t the c o r r o s i v i t y c h a r a c t e r i s t i c . " Consequently, t h e i r d i l u t i o n or n e u t r a l i z a t i o n i n accordance with EPA s operating c o n d i t i o n s does not r e q u i r e an i n d i v i d u a l RCRA permit provided, o f course, they are not part of an i n d u s t r i a l waste stream which has been designated as hazardous (52). I t should be noted t h a t , as o f t h i s w r i t i n g , the permit requirement i s only suspended, and the permit by r u l e i s not yet i n e f f e c t . Current EPA r e g u l a t i o n s should be reviewed concerning f u r t h e r developments and concerning a l l other a p p l i c a b l e requirements. f


SOLUBLE

44

SILICATES

I f a h i g h l y a l k a l i n e sodium s i l i c a t e waste i s c l a s s i f i e d as a hazardous waste under RCRA, i t i s a l s o a hazardous substance under the Comprehensive Environmental Response, Compensation and L i a b i l i t y Act of 1980 (CERCLA or Superfund A c t ) . The law s r e p o r t i n g requirements would apply to any r e l e a s e i n t o the environment. This i s a l s o true for the p r e v i o u s l y mentioned sodium o r t h o s i l i c a t e products which are EPA hazardous substances, s i n c e they are p h y s i c a l mixtures c o n t a i n i n g sodium hydroxide. For sodium hydroxide the r e p o r t a b l e quantity remains I, 000 l b . U n t i l r u l e s to implement the act are published, the r e p o r t a b l e quantity o f a c o r r o s i v e waste i s 1 l b . Downloaded by GEORGETOWN UNIV on June 25, 2016 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch003

f

Toxic Substances C o n t r o l Act Following Chemical Abstract Service terminology, the commercial s o l u b l e s i l i c a t e s were reported to the i n i t i a l inventory of e x i s t i n g chemical substances as i n d i c a t e d i n Table II. Under the r e p o r t i n g r u l e s (53), a hydrated chemical was to be regarded as a mixture, and the anhydrous substance was to be reported. The only subsequent r e g u l a t o r y development thus f a r under TOSCA, d i r e c t e d s p e c i f i c a l l y at s o l u b l e s i l i c a t e s , was a proposed r u l e (54) under Section 8(a) which would r e q u i r e manufacturers to keep c e r t a i n records and report production and exposure r e l a t e d data on approximately 2300 chemicals to EPA. This information was held to be necessary to rank chemicals f o r i n v e s t i g a t i o n and to make p r e l i m i n a r y r i s k assessments. Sodium s i l i c a t e , potassium s i l i c a t e , sodium m e t a s i l i c a t e and sodium o r t h o s i l i c a t e were included on the candidate l i s t , presumably because r e p o r t s to the i n i t i a l inventory showed them to be manufactured i n high tonnage volume. It i s now understood that the l i s t has been pared down to about 300 chemicals. In view of the p u b l i c a v a i l a b i l i t y of previous h e a l t h hazard assessments by FDA, IJC and others, which has been pointed out to EPA i n comments on i t s proposal, i t i s expected that the s o l u b l e s i l i c a t e s are among the chemicals which have been s l a t e d to be e l i m i n a t e d from the l i s t . Discussion I t has been seen that even r e l a t i v e l y simple and f a m i l i a r chemicals l i k e the s o l u b l e s i l i c a t e s have become quite e x t e n s i v e l y involved i n the v a r i o u s r e g u l a t o r y schemes designed to p r o t e c t our h e a l t h and environment. The reason i s t h e i r high tonnage production and t h e i r broad d i s t r i b u t i o n , ranging from i n d u s t r i a l plants to the home. The s o l u b l e s i l i c a t e s are t r u l y r e c y c l e d by man: they d e r i v e e n t i r e l y from mineral d e p o s i t s and are returned to the


Current



Table I.

Regulatory

Status

Typical Impurity Levels in Commercial Sodium Silicates (ppm, ppb where noted)

Soluble Silicates - ACS Publications - American Chemical Society

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