ES&T LETTERS Organohalogen compounds in nature Dear Editors: Gordon Gribble made a very clear and concise statement in his letter [ES&T, Dec. 1993, p. 2620) on the review "In Situ and On-Site Bioreclamation" by Frederickson et al. [ES&T, Sept. 1993, p. 1711). He stated that the preva lent apprehension that "Organohalogens are rarely found in nature . . ." is no more than a red herring. To that, Frederickson et al. replied: "To our knowledge, significant quantities of naturally occurring organohalogens are not found in soil, sediment, or groundwater." We would like to comment on the oc currence of naturally produced organohalogens in soil. The past few years of research have clearly shown that naturally produced organically bound halo gens are widespread in soil, surface water, and groundwater and that large amounts are stored in soil and sediments. This subject was ad dressed in our ESB-T feature article (Aug. 1991, p. 1346). The major fraction of the organically bound halogens in soil has not been identi fied (i.e., the 400,000 tons detected in Swedish peat bogs that Gribble referred to are unidentified organi cally bound halogens that were de tected as AOX in peat leachates) (2). Apparently, most of the organohalogens in soil are high molecular weight compounds. We have, in fact, been able to identify chlori nated structural elements in natural humic acids (2). Through an unfortunate formula tion in the comment made by Grib ble it appears as if the origin of these compounds is well known. Two po tentially important sources have ac tually been suggested: halometabolite production and exo-enzymemediated halogenation (3), but the relative contribution from these or other sources is not known. References (1) (2) (3)
Asplund, G.; Grimvall, Α.; Pettersson, C. Sci. Tot. Environ. 1989, 81-82. 2 3 9 48. Dalhman, O. et al. Environ. Sci. Technol. 1993, 27, 1616-20. A s p l u n d , G.; C h r i s t i a n s e n , J. V.; Grimvall, A. Soil. Biol. Biochem. 1993, 25, 41-46. Gunilla Asplund Anders Grimvall Linkôping University, S w e d e n
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In deriving the soil standard, RIDOH used an equation similar to the one p r e s e n t e d by Wixson and Davies (that is, S = [(Τ - B)R]/[dI] where S is the standard for soil, paint, and dust; Τ is the target blood level; Β is the background blood lead level; R is the relative source contribution (%); d is the factor be tween blood lead level increase and the amount of lead ingested; and I is the rate of ingestion of dust, soil, and/or paint). Both approaches de Lead in soil rive standards as a function of the difference between the target and Dear Editors: We commend Wixson and Davies for summarizing recom- background blood lead level. How ever, we disagree with the authors' mendations of the Society for Envicontention that the geometric stan r o n m e n t a l G e o c h e m i s t r y and dard deviation of the underlying Health's "Lead in Soil" Task Force (ES&-T, January 1994, p. 26A). This blood lead distribution is the appro priate statistic for predicting the report provides timely guidance to percentage of children protected by state and federal agencies faced the standard. Also, we feel that the with legislative mandates to deauthors did not adequately address velop standards for acceptable levissues regarding variability in soil els of lead in soil. We support many ingestion rates. of the points raised by the authors and feel some discussion is warIn developing a soil standard for ranted on the points of contention lead, it must be kept in mind that as well. lead poisoning can result from ei Wixson and Davies' report prother acute or chronic exposures. vides a clear demonstration of the Children typically progress through public health impacts associated a series of stages during their devel with setting a standard for lead in opment, with some of these stages soil. Summary tables provide regucharacterized by a dramatic in lators with a tool for translating a crease in mouthing behaviors and public health goal into a specific soil ingestion rates. Also, some chil soil standard. Based on our experidren, especially those who display ence of establishing lead standards pica, may ingest several grams of in Rhode Island, members of the soil each day. Wixson and Davies' public and representatives from failure to mention either of these is community, business, and trade assues is a major omission. sociations can reach consensus on In addition, we question the au goals for an acceptable target blood thors' use of the factor "G n ," an ex lead level for children, and for the ponential of the geometric standard degree to which a standard must endeviation of blood lead distribution, sure that each child is protected for deriving soil standards. The geo from lead poisoning. We concur metric standard deviation of the with the authors' recommendation blood lead distribution for 26,000 that industrial and child-care areas samples analyzed in Rhode Island be subject to different standards. in 1993 is 2.2, far outside the range Also, we have found broad public of values predicted by the authors. acceptance for the authors' sugUsing the authors' equation for de gested soil remediation measures, riving s t a n d a r d s results in ex which include tilling, revegetation, tremely low and impractical stan and barrier construction. These are dards when values greater than 2.0 desirable, practical alternatives to are substituted for G We have little removal and replacement of conconfidence that this statistic is rele taminated soil. vant to Rhode Island's soil stan dard. Factors relating to the degree In February 1992, the Rhode Isof vegetative cover, the range of soil land Department of Health (RIDOH) ingestion rates in the target popula promulgated the Rules and Regulation, and other factors that directly tions for Lead Poisoning Prevention (R23-24.6-PB), which includes stan- relate to soil lead exposures seem better predictors of the percentage dards for lead in soil, interior and of children protected by specific exterior dust, paint, and water (2).
Environ. Sci. Technol., Vol. 28, No. 9, 1994
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soil standards. Although factoring G into the derivation of soil standards may indirectly address these issues, w e are c o n c e r n e d t h a t r e g u l a t o r s may incorrectly predict that a given s t a n d a r d is p r o t e c t i v e of 9 5 % of children w h e n actually it only pro t e c t s c h i l d r e n for 9 5 % of t h e i r childhood, a far less desirable out come. The RIDOH, w i t h considerable as s i s t a n c e from its E n v i r o n m e n t a l Lead Advisory Committee, devised a tiered a p p r o a c h for s e t t i n g soil s t a n d a r d s (1). " L e a d - f r e e " s t a n d a r d s w e r e d e r i v e d as d e s c r i b e d above. P e r m i s s i b l e or " l e a d - s a f e " levels were set at medium-specific c o n c e n t r a t i o n s , w h i c h are h i g h e r t h a n the respective lead-free stan dards, but were designed to afford children the same degree of protec tion from poisoning. This is accom p l i s h e d by linking the higher envi r o n m e n t a l level to implementation of simple, inexpensive control mea sures. In Rhode Island, soils below 150 p p m are d e f i n e d as lead-free and require no controls. Soil is de fined as lead-safe between 150 a n d 500 p p m if behavioral controls, e.g., e d u c a t i n g r e s i d e n t s about h o w to limit dust generation and excessive soil ingestion, are in place. F r o m 500—1000 p p m , a mix of behavioral a n d e n v i r o n m e n t a l c o n t r o l s (e.g., m a i n t a i n i n g grass cover) are man dated for m a i n t e n a n c e of a lead-safe status. From 1000 to 10,000 p p m , behavioral controls are inadequate. Soil levels must be lowered or soil m u s t be covered. It is not until soil levels reach 10,000 p p m that soil re moval and r e p l a c e m e n t are re quired. It is still too soon to deter m i n e if t h i s a p p r o a c h is b o t h w o r k a b l e a n d p r o t e c t i v e of c h i l dren's health. Reference (1) Boulay, L. Α.; Vanderslice, R. R.; Matyas, Β. Τ. "A Rational Basis for Devel oping Lead Standards in Regulation"; Abstract #3090. Presented at the 121st Annual Meeting of the American Pub lic Health Association, Oct. 24-28, San Francisco, CA, 1993. Robert R. Vanderslice Lynn M. Boulay Bela T. Matyas Rhode Island Department of Health Providence, RI 02908-5097 Authors' response T h a n k s for your comments and con cerns on our article s u m m a r i z i n g the Society for Environmental Geo chemistry a n d Health (SEGH) task force report on "Guidelines for Lead
in Soil." We have received very fa v o r a b l e c o m m e n t s on t h e general a p p r o a c h a n d urged that other data a n d models s h o u l d also be consid ered in using the matrix a p p r o a c h p r o p o s e d in the SEGH models. The SEGH task force hopes that any val ues chosen s h o u l d be modified with ongoing or future research w h e n us ing the suggested guidelines w h i c h are theoretical calculations. The concern for soil ingestion is addressed in detail in the full SEGH r e p o r t ( a v a i l a b l e from St. L u c i e Press C o r p o r a t i o n , 100 E. L i n t o n Blvd., S u i t e 4 0 3 B , Delray Beach, FL) a n d i n c l u d e s a table of " s o i l s t a n d a r d s " set u p o n the basis of the a m o u n t of soil ingested per day. In discussing your data with other m e m b e r s of our task force, it w a s felt that as a public health measure, we should stand by our a p p r o a c h in protecting the majority of children. Eating large a m o u n t s of soil is rela tively rare, as is true pica for soil, i.e., m o r e t h a n just sticking dirty fingers or toys in one's m o u t h . So, if the p h i l o s o p h y is to protect every child then very restrictive standards w o u l d need to be set. Clifford D. Strehlow, SEGH task force m e m b e r from C h e l s e a a n d W e s t m i n s t e r H o s p i t a l in L o n d o n , evaluated your data and suggested that your high GSD of 2.2 seemed to i n d i c a t e a p o p u l a t i o n e x p o s e d to m u l t i p l e sources of lead a n d not just lead from soil a n d dust. If you are screening population groups at high risk from exposure to lead in paint, for example, our equations cannot, of course, be applied directly. Broad or multipeaked blood lead distribu tions w o u l d appear to confirm mul tiple lead sources. According to Strehlow, you may have a m u l t i m e d i a exposure frame, which would need a multimedia c o n t r o l s t r a t e g y . E x p o s u r e s to sources other t h a n soil m u s t be fac tored out. As a first approximation, the b a c k g r o u n d term, B, could b e increased. However, the blood lead and exposure data for the lead-inp a i n t risk g r o u p s h o u l d b e sepa rated from the Rhode Island data be fore e x p o s u r e i n s o i l (a m a j o r portion of your data) can be prop erly assessed. Bobby G. Wixson Clemson University Clemson, SC 29634-1901 Brian E. Davies Correction We regret the omission from the Au gust issue of a cover photo credit for Radian Corporation.
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