Preliminary pollutant limit values for In the environmental fate model for soil artd water, the allowable pollution level in the soil is determined by the acceptable daily intake in man
~
Jack C. Dacre David H. Rosenblatt U S . Army Medical Bioengineering Research and Development Laboratory Ft. Detrick, Frederick, M d . 21 701 David R. Cogley GCA Corporation Bedford, Mass. 01 730 The time interval between'first disclosure of planned pollution regujations and required compliance with these regulations by industry is often short; responsible industries sometimes need to anticipate pollution standards that will eventually be set. Through projection of a probable pollution limit range for a given substance, the planning, development, and institution of operational controls can be accomplished in a reasonable time period. A preliminary pollutant limit value (PPLV) concept has been developed to predict probable environmental limits for pollutants. The PPLV is a temporary, nonregulatory value that is based on information available in the literature and that relates primarily to human health effects. The PPLV concept is described more fully in a chapter of a forthcoming book ( 1 ) . Feature articles in ES&T hace by-lines. reprecent the ciews o f t h e authors, and are edited by the Washington staff. If you are interested in contributing an article, contact the managing editor. 778
Environmental Science & Technology
Human beings may be exposed to pollutants by several routes, as shown schematically for soil via water in the box material. For each of these routes, a single-pathway PPLV (SPPPLV) can be calculated. The PPLV concept treats each possible pathway as a series of compartments; equilibria are assumed to exist between successive compartments, except between the next-to-last compartment and man. The last step in this pathway usually depends upon dietary intake. The final PPLV is derived by normalizing all SPPPLVs. Common sense should always be exercised in the derivation and use of PPLVs. These values should always be derived with careful consideration of the site-specific conditions. The PPLV model should be regarded as a framework that can be modified to account for site-specific elements. The temptation to develop and institutionalize PPLVs as standards should be avoided. Each value should be given a mandatory date for reconsideration, and the data base used in the formulation should be continually updated and examined. An experimental approach to determining environmental pollutant standards is certainly preferable to the extensive reliance on assumptions that characterizes the PPLV procedure; the principal merit of the PPLV is that it can be determined even in the absence of complete data. Where data gaps are sufficient to warrant experimental research, available resources can be
properly allocated by specifying research only for key parameters identified by the PPLV-determination process.
Derivation of PPLVs The PPLV is determined in six steps: Pollutants and pathways are identified. An acceptable daily dose of toxicant ( D T ) and partition (intermedia transfer) coefficients are determined or estimated. Relevant data are gathered from the literature. SPPPLVs are calculated for all pathways (not site-specific). Critical pathways for each pollutant are selected (often site-specific). The PPLV is derived by normalization of SPPPLVs. Normalization adjusts the pollutant concentration where pathways originate in the same medium or have a common point of intersection. A simple calculation, similar to adding electrical resistances in parallel DC circuits, is used, such that SPPPLVs taken together provide the target organism, man, with an exact DT. The following equation describes the calculation of a PPLV from SPPPLVs via three pathways from water: PPLV = 1 + [l/(SPPPLV), l/(SPPPLV)* I/(SPPPLV)3] (Eq. 1) The approach used in calculating
+
+
0013-936X/80/0914-0778$01 .OO/O @ 1980 American Chemical Society
Pathways from soil via water, plant, and animal compartments to mana
6B -#e---==Water
Root crop
\
Water
@ Moisture
69 69 Water
Water
0 Hydrosoil
Moisture
@ Moisture
Atmospheqparticles)
In this fate model, the acceDtable dailv dose of toxicant. DT.can be obtained from six sources of literature information. The eauation for calculating the acceptable daily dose IS’: DT = f x DFI x Ca = K p a x Kwp x Ksw x C, x f x DFliBW (fq.2) BW i
a
‘See Table 2 for definitions of the abbreviations
SPPPLVs assumes contaminants to be in stepwise equilibrium (steady state) from source to receptor. Although the model has been applied here to humans, it is equally applicable to plants and wildlife. Any part can be modified as required, without necessarily invalidating the other parts. For example, pollutant residues in fish are considered to exist in equilibrium with pollutant concentrations in water. However, bottom feeders, such as catfish, may actually be in equilibrium with residues in sediments. The calculation procedure can be tailored to accommodate such a situation. The SPPPLV calculations utilize certain standard parameter values for chronic human exposures (Table 1). In exceptional cases, the calculations could take into account sensitive
subgroups within the population, such as embryos, infants, and aged individuals. Human beings are exposed to toxic materials by surface contact, inhalation, or ingestion. Because surfacecontact doses that produce toxic effects are usually so much higher than ingestion or inhalation doses that produce similar effects, the percutaneous route is not considered in the calculation of PPLVs. To further facilitate the calculation, the DT is considered to be the same for exposure by inhalation as for ingestion, with a few, usually apparent, exceptions (such as hydrogen chloride). Where human receptors are distant from the site of contamination, it may be feasible to take into account loss of pollutant through dilution, volatiliza-
tion, hydrolysis, biodegradation, and phototransformation.
Establishing partition coefficients The PPLV model assumes that between any two adjacent media (compartments), the pollutant is partitioned in a perfectly constant manner. The box material represents a particular pathway from source to human receptor. Maximum concentration values and pseudosteady-state conditions between media are presumed. The last step involves no assumed equilibrium, but depends on the ingestion rate. With reference to the notation in Table 2, the relationship between the acceptable daily dose of toxicant (mg kg-’day-’), DT,and the limiting pollutant level in soil (mg kg-I), C,, is given by the following equation: Volume 14, Number 7, July 1980
779
DT =
TABLE 1
Parameter values for human chronic exposure .70 kg Body weight (BW)a ........................ 24-Hour breathing rate (RB)* . . . . . . . . . . . . . . . . ..18.5 m3/24 hour . . . . . . . . . . . . . . ..12.1 m3/8 hour Workday breathing rate Daily food intake (DFI), dry weight basisC . . . . . . . .OB3kg day-’ Daily water intake ( Ww)a .................... .2 kg day-’ (2 L day-’) Temperature ( T ) , unless otherwise stated . . . . . . . .25 O C (77 OF) 4The Safe Drinking Water Committee of the N a t i i l Research Council (2)used the 7akg person and 2 L/day as average values. * Average breathingrates were obtained from Clelandand Kingsbury (3). According to Aibritton (4,dairy food intake figures vary somewhat from one informationsoufee to another as well as between men and women.
AD1 BW
= Acceptable daily intake, mg kg-’ day-’
Ca
= Body weight (human), kg = Limiting concentration of pollutant in a food animal, typically
CP
= Limiting concentration of pollutant in a crop used for human or
cs
= Limiting pollutant level in soil for human health effects, mg kg-’
CSf Csi
= Final C, value (a PPLV), mg kg-‘ = Initial C, value (an SPPPLV), mg kg-’ = Limiting pollutant level in water for human health effects,
cattle, mg kg-’ meat-animalfood, mg kg-’
cw Cwf cwi
DFI
4 f
mg L-’ = mg kg-‘ = Final Cwvalue (a PPLV), mg L-’ = mg kg-’ = Initial Cwvalue (an SPPPLV), mg L-’ = mg kg-’ = Daily food intake, kg day-’ = Acceptable daily dose of a toxic substance, mg kg-’ day-’ = Fraction of total diet representedby food of a given type
KWa
= ca/cp = cp/cs = CwICs = CaICw
Kwf
= Concentration in fish/ Cw, i.e., bioconcentration factor
KWP LD50
= cp/cw = Singledose level that kills 50% of a group of test animals of a
Kpa KSP Ksw
NELQo PPLV
given species (and preferably strain and sex) with 14-day observation of the animals, mg kg-’ = Maximum contaminant level (provisional water limit) in water, mg L-’ = mg kg-’ = Lifetime (chronic) no-effect level, mg k g ‘ day-’ = 90-Day (subchronic) no-effect level, mg kg-‘ day-’ = Preliminary pollutant limit value, m~ L-’ or mg kg-’
PPm
= Parts per million (mg L-’ in water; mg kg-’ in soil, food, or
RB
= Breathing rate, volume of air breathed by a 70-kg human being
RB’
= Breathing rate, volume of air breathed by a 70-kg human being
MCL NELL
living organisms) in 24 hours, m3 day-’
in an 8-hour workday, m3 day-’ SPPPLV = Single-pathway preliminary pollutant limit value, mg L-‘ or mg kg-‘ T = Temperature, degrees Kelvin = Threshold limit value for occupational exposure to toxic airborne TLV pollutants over a 40hour week, mg m-3 (or ppm)a = Daily water intake, L day-’ = kg day-’ W W e
780
mg m--3 = ppm X MW124 at 25 O C .
Environmental Science & Technology
BW = Kp, X KwpX K,, X C, X f X DFI/BW (Eq. 2)
The bottom part of the equation is derived from the definitions:
c w = KSWC,
(Eq. 3)
Cp = KwpCw
(Eq. 4)
(Eq. 5 ) By inversion of Equation 2, the SPPPLV in soil by the pathway shown in the box material can be calculated as follows: Ca = KpaCp
TABLE 2
Symbols and abbreviations involved in the calculations
f X DFI X C,
cs
= (BW
x DT)/(Kpa x Kwp
X K,, X f X DFI)
(Eq. 6) The following values off might be used in the absence of better sources of information ( 5 ) : 0.1 for any one crop (e.g., root, grain, fruit); 0.2 for meat; 0.05 for fish. These values are estimates and should not be otherwise construed. The assumption that equilibria exist between successive compartments in these pathways is seldom true, because equilibrium is rarely achieved and because the equilibrium ratio need not be constant for all concentration levels. Information for establishing the partition coefficient can be difficult to find, and one must often accept a single literature value as typical of a given intermedia transfer. Caution should be exercised in applying such values; they may vary with local conditions, such as soil type. When no pertinent information can be found, one may use algorithms that relate soil-water partition coefficients (6) and water-fish partition coefficients (7) to octanolwater partition coefficients. The latter can be estimated for most organic compounds from structural fragment constants and algorithms available in the literature (8). When no source is available from which to calculate a given partition coefficient, let K = 1. A partition coefficient is not required for the transfer of pollutant between the final medium and man.
Establishing & values The determination of DT values is essential to the calculation of PPLVs. DT values may be obtained from six sources, which are listed in order of preference in Table 3. When available, the World Health Organization acceptable daily intake (ADI) value should be used as DT. When this value is not available, the maximum concentration level (MCL) value for drinking water established by the U S . Environmental Protection Agency
An overview of the current state of the chemical sciences in China as seen through the eyes of 12 leading American chemists A Trip Report of the U.S. Delegation in Pure and Applied Chemistry John D. Baldeschwieler, Editor, California lnstitute of Technology Foreword
by Glenn T. Seaborg, University of California at Berkeley
Fully illustrated with photographs, charts, and diagrams, this fascinating report offers a current look at the status of research, development, and teaching programs in chemistry and chemical engineering observed by the 12-member U.S. Delegation in Pure and Applied Chemistry during their three-and-onehalf week visit to the People's Republic of China in May and June of 1978. Distinguished chemists and science administrators from the Delegation deftly chronicle the exciting chain of events: a trip to the U.S. by a delegation of Chinese scientists in April and May 1977.. .plans for a reciprocal visit to the PRC by the U.S. Pure and Applied Chemistry Delegation. . .the precedent-setting journey to Peking. . .multi-course banquets punctuated by traditional Chinese toasts, followed by talks by Delegation members on their areas of expertise. . .visits to laboratories, educational institutions, and industrial plants in Peking, Tach'ing, Shanghai, Hangchow, Sian, and Lanchow. . .and finally, the group's return home after becoming acquainted with the overall state of the chemical sciences in China today-providing a base for future exchange of scientific information through joint symposia, visiting scholars, and joint research programs. A vital book for those interested in this expanding world and for those who may seek market or research information in this recently opened area.
266 pages hardback $1 5.00 paperback $ 9.50
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CONTENTS Roots of Chemical Research and Development in China The Institutional Structure of Chemical Research and Development in China Chemistry and Chemical Engineering in the Context of National Science Policy Chemistry and Chemical Engineering as Elements of Science Education in China Basic Research in the Subdisciplines of Chemistry and in Chemical Engineering Status of Research in Key Areas of Technology Organization of Chemical Research and Development in Broad National Mission Areas Infrastructure Discussion Recommendations
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Volume 14, Number 7, July 1980
781
may be converted to DT by using the parameter values for human chronic exposure given in Table 1:
DT = (MCL X Ww)/BW = MCL/35.
(Eq. 7)
Threshold limit values (TLVs), published by the American Conference of Governmental Industrial Hygienists, can be converted to DT in three steps: dividing by (24 X 7)/(8 X 5) = 4.2 to convert from a normal 5-day, 8-hour/day, work week to continuous exposure; dividing by 100 to allow for exceptionally sensitive individuals who would not normally be part of the work force and to account for the involuntary and unsuspecting nature of the exposure; and converting TLV (expressed in mg m-3) to a total dose. For the last factor, the breathing rate, RB’, for a 70-kg person doing light work is taken as 12.1 m3 per 8-hour day, as shown in Table 1 . Hence:
DT = (TLV X RB’)/(420
X BW)
= TLV/2430
(Eq. 8)
There is one important caveat for using converted TLV values. When TLV values were chosen, they were not permitted to exceed 1000 ppm, except for carbon dioxide ( 1 1 ) . Thus, if the TLV is 1000 ppm (or its equivalent in mg/m3), the actual safe level of exposure, and therefore the DT,may be higher. It is also necessary to consider whether the TLV is strongly related to a degree of lung irritancy not likely to be translated, after ingestion, to systemic toxicity. The remaining three sources from which DT might be derived are from animal experiments. Although similar experiments were the ultimate source of the first three methods for calculating DT,the toxicological experiments referred to here have not gone through the process of extrapolation, evaluation, and consensus. Thus, they should be used only when better numbers are lacking. The no-effect level from a chronic or lifetime study in a laboratory animal (NELL) is diminished by a factor of 100 (12) to account for interspecies differences and especially susceptible individuals or groups within the population:
DT = N E L L X l o v 2 (Eq. 9) The no-effect level from a subchronic (90-day) study requires an additional safety factor of 10 because of the shorter period of exposure
(f2):
DT = NEL90
X
(Eq. 10) 782
Environmental Science & Technology
The most likely toxicity value to be found in the literature is LD50, usually for rats or mice. There is seldom enough information to permit extrapolation of LD50 to a dosage at which only a very small fraction (e.g., 1%) of the animals would be killed, or to determine an acceptable risk level. Handy and Schindler ( 1 4 ) assume a safe limit for the continuous body concentration of a toxic substance to be 5 X X LD50. Based on experimental studies, they also assume a biological half-life of 30 .days, which implies a disappearance rate of 2.3 1% per day. If the daily intake of the toxic substance is made equal to the daily disappearance rate a t the safe concentration limit, then that safe concentration is maintained:
DT = 2.31 x 10-2 x 5 x 1 0 - ~ X LD50 = 1.155 X X LD50 (Eq. 11)
Calculation of single-pathway values For pollutants originating in surfacr water or groundwater. It is obvious that a calculated PPLV (for an aqueous solution of the pollutant) has little meaning if it is greater than the solubility of the pollutant. However, an SPPPLV above the solubility should be kept in the calculations until the PPLV is obtained by normalization, since the latter could still be less than the solubility value. Ingestion of water
c, = BWWW DT = 35 DT (Eq. 12) This equation is based on the assumption that the water has undergone filtration or settling to the extent that particles are not likely to be ingested. Alternatively, C, = MCL. Fish ingestion X DT c, = f XBW DFI X K,f (Eq. 13) The value K,f represents a bioconcentration factor in fish; since bioaccumulation in aquatic organisms occurs almost entirely through water contact, not through food, it is usually true that the estimated value of C, is not affected by the position of the fish in the food chain. Water used for irrigation or pond culture of plants for human consumpX DT tion c, = f XBW DFI X K,, (Eq. 14) Because sources of food in the U.S. are normally quite diverse, a value of
f of 0.1 may be used to represent a food crop grown in water contaminated with a unique (not widespread) pollutant. Values of K,, are usually close to unity. Thus, a calculation embodying the above assumptions along with the parameters listed in Table 1 would give C, = 11 11 DT.K,, may tend to be higher for a root crop than for a grain or leafy vegetable. Water used to irrigate crops for consumption by food animals (crops assumed to be 100% of the animal diet) BW X DT = f X DFI X K,, X K,, (Eq. 15) If food animals consume polluted water and the value of K,, is low, it may be better to consider the direct water-animal equilibrium involving Kwa ( C a / C w ) and ignore the plant compartment. Since data for K,, and K,, are not often found, one might be tempted to use the equivalents K,, = K,f and Kpa = K,f/K,,. However, use of these equivalents may be inappropriate. In the case of cattle, if K W p< 1, the route soil-water-plant-animalman can be ignored; if K,, > 10, the route soil-water-animal-man can be ignored. The two routes might be considered together when 1 < K,, < 10. Water to respired air This pathway is not ordinarily significant and would require complex calculations beyond the scope of this article. It might be useful in some special contexts, such as that of a relatively volatile, not overly soluble material of high toxicity in a large waste-disposal lagoon. For pollutants originating in soil and transferred through water. The calculation of an SPPPLV or a PPLV for soil through water implies a concentration of pollutant in the water phase, C , = K,,C,. Should C, be greater than the solubility of the pollutant (after normalization), then no concentration in the soil would be high enough to provide a toxic level to human beings solely by the soil-water routes. Soil leached into groundwater that is eventually ingested BW X DT c, = K5w 35 DTIK,, X Ww
Soil used to grow crops for human consumption X DT c, = K , , X BW K,, X f X DFI
or
c, = K,,B XWf XXDT DFI (Eq. 18) Soil leached by water to be used by food animals
c, = K,,
B W X DT X K,, X f X DFI
(Eq. 19) Soil used to grow crops fed to or grazed by food animals (crops assumed to be 100% of the animal diet)
c, = K,,
I (NEL)
BWXDT X K,, X K,, X f X DFI
Use safety factor of lo2 Use safety factor of
io3
Use safety factor of -IOJ
( 12) ( 12) ( 13, 14)
or
c, = K,,
B W X DT X K,, X f X DFI
(Eq. 21) Grazing animals in pasture may consume a considerable amount of soil if they graze close to the ground. An estimate of soil ingested would have to be made and used for a new calculation. River sediment via water and fish flesh
c, = K,,
B W X DT X K,f X f X DFI
(Eq. 22) For pollutants originating in the upper layers of soil and transferred by respiration. Pollution dispersion through air presents an extremely complex case for determination of SPPPLVs. Some of the local factors affecting such an analysis will be discussed in a forthcoming publication (1).
Last step-normalization of SPPPLVs to PPLVS A pollutant is most likely to be found in soil and associated groundwater. Thus, each value for soil can be converted to an SPPPLV for water (see Table 2 for notation): C,i = KswCsi
(Eq. 23)
Each value for water can be similarly converted to an SPPPLV value for soil: Csi = Cwi/Ksw (Eq. 24) It is important that each pathway be represented once and only once. For example, if ingested water is considered both as polluted groundwater and as leachate from soil, the total water ingested is still 2 L/day, and the water ingestion pathway is only represented
once. A PPLV is calculated (with C,; values being SPPPLVs C,, , Cw2,etc.) as follows:
C,f = 1 +
n
i= 1
l/C,,
(Eq. 2 5 ) Thus, if C,i were 10 ppm by water ingestion, 5 ppm by fish ingestion, and 20 ppm by crop ingestion, then the PPLV would be: C,f = 1 + (Y5
+
+
%o ‘/20) = 2.86 ppm (Eq. 26)
If C,f, by this calculation or by: C w f = KswCsf (Eq. 27) were higher than the solubility of the pollutant in water, and all probable pathways had been adequately considered, it would be unnecessary to set a PPLV. This procedure assumes that the ingested water would be free of suspended particles.
Summation The approach described in this article must be considered a conceptual framework within which to provide environmental decisions. One should not be surprised therefore if two environmental engineers obtain different results from analysis of the identical situation. This may be the result of valid differences in judgments. Further, the present treatment is only a beginning-a springboard for examination of other critical areas, such as air pollution derived from sources in soil and water, and effects on aquatic organisms. References (1) Rosenblatt, D. H.; Dacre, J. C.; Cogley,
D. R. “An Environmental Fate Model Leading to Preliminary Pollutant Limit Values for Human Health Effects”, In
“Environmental Risk Analysis for Chemicals”; Conway, R. J., Ed., Van Nostrand Reinhold Co.: New York, 1980, in press. (2) National Research Council, “Drinking Water and Health”; National Academy of Sciences: Washington, D.C., 1977, pp 11, 498. (3) Cleland, J. G.; Kingsbury, G. L. “Multimedia Environmental Goals for Environmental Assessment, Volume I”, EPA 60017-77-136a: U S . Environmental Protection Agency: Washington, D.C., Nov. 1977, pp 60-61. (4) Albritton, E. C., Ed. “Standard Values in Nutrition and Metabolism”; W. B. Saunders Company: Philadelphia, 1954, pp 48-57. (5) Albritton, E. C., Ed. “Standard Values in Nutrition and Metabolism”, W. B. Saunders Company: Philadelphia, 1954, pp 75-76. (6) Kenega, E. E.; Goring, C. A. I. “Relationship Between Water Solubility, SoilSorption, Octanol-Water Partitioning, and Bio-concentration of Chemicals in Biota”, In “Third Aquatic Toxicology Symposium”; American Society for Testing and Materials: Philadelphia, 1980, STP 707, pp 78-115. (7) U S . Environmental Protection Agency, “Water Quality Criteria”, F e d . Regist. 1978,43 (May l a ) , 21506-18. (8) Rekker, R. F. “The Hydrophobic Fragmental Constant”; Elsevier Scientific Publishing ComDanv: Amsterdam/Oxford/Newkork, 1877.(9) World Health Organization, “Evaluation of the Toxicity o f a Number of Antimicrobials and Antioxidants”; Sixth Report of the Joint FAOnVHO Expert Committee on Food Additives, WHO Tech. Rep. Ser. NO.228, pp 9-11,1962. (10) U S . Environmental Protection Agency, “National Interim Primary Drinking Water Regulations”, Fed. Regist. 1975,40 (Dec. 24), 59565-88. (11) American Conference of Governmental Industrial Hygienists, “Documentation of the Threshold Limit Values (for Substances in Workroom Air)”, 3rd ed.; American Conference of Governmental Industrial Hygienists: Cincinnati, 1974. (12) Vettorazzi, G. “Safety Factors and Their Application in the Toxicological Evaluation”, In “The Evaluation of Toxicological Data for the Protection of Public Health”; Hunter, W. J.; Smeets, J. G. P. M., Proc. Int. Colloq., Commission of the EuVolume 14, Number 7, July 1980
783
ropean Communities, Luxembourg, 1976, Pergamon Press: Oxford/New York, 1976, pp 207-23. (13) Lewis, R. J., Jr.; Tatkem, R. L., Eds. “Registry of Toxic Effects of Chemical Substances, 1978 Edition”; DHEW (NIOSH) Publication No. 79-100,National Institute for Occupational Safety and Health: Cincinnati, 1979. (14) Handy, R.; Schindler, A. “Estimation of Permissible Concentrations of Pollutants for Continuous Exposure”, EPA 600/276-155; U.S. Enxiironmental Protection Agency: Washington, D.C., June 1976, p 61.
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Jack C. Dacre is now toxicological advisor and research toxicologist at the US.Army Medical Bioengineering Research and Development Laboratory, Environmental Protection Research Division, Ft. Detrick, Frederick, M d . Dr. Dacre is also a consultant and member of the W H O Expert Advisory Panel on Food Additives and Pesticide Residues. H e has some 100 publications on toxicological, biochemical, and metabolic f a t e studies of f o o d additives, f o o d colors, pesticides, and environmental chemicals, especially munitions products, fungal metabolites, and trace metals. H e received his Ph.D. in biochemistry in 1950 f r o m the University of London (London School of Hygiene and Tropical Medicine).
David H. Rosenblatt ( I ) is currently chemistry advisor in the Environmental Protection Research Division of the U S . A r m y Medical Bioengineering Research and Development Laboratory, Ft. Detrick, Frederick, M d . His research interests range f r o m organic chemical mechanisms t o the physicochemical behavior and transport of environmental contaminants. H e received his Ph.D. in chemistry f r o m the University of Connecticut. David R. Cogley ( r ) is the acting manager of the Toxic and Hazardous Materials Section of GCAITechnology Division, Bedford, Mass. He has directed: studies of the environmental effects of hazardouswaste disposal at a large military installation: the preparation of environmental impact statements f o r coal-fired steamelectric generating stations: and studies of municipal aquifer contamination by industrial solvents. H e received his A.B. f r o m Haruard College and his Ph.D. in physical organic chemistry f r o m Brandeis University.
Turn to sodium borohydride for the capability to recover these valuable raw materials and to reduce discharge limits to well below typical standards: Mercury-0.04-0.2 mgA Lead less than 0.1 mg/l Silver less than 0.1mgA Copper- less than 0.1mgA. In actual industrial applications, SBH enables manufacturers to recover metals in a more usable form than other removal methods, Free of troublesome by-products; while significantly reducing or even eliminating the need for expensive disposal methods. SBH can remove a broad range of heavy and precious metals from both process solutions and waste streams. It is fast, effective, energy efficient and typically requires little or no capital investment. And the value of the recovered metal can often more than offset treatment cost. Send today for complete information, or call George Medding. He’ll help you turn heavy metal disposal problems into profits!
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