Document 85eab9pKv0616Yr8NDn52qV7a

to that encountered in natural environments and, probably, most coniiparable to high-energy environments. If a dower stirring rate were used, resulting in a lower shear, the floes Figure 1. Size distributions for kedinlte floes in the Mskln bottle end after removal from the outlet with gentle handling and with normal handling. Figure 2. Size tistrfcutions for floes of natural sample In Nlskln bottle and after removal from the outlet with gentle handing and with normal handing. . water free falling 5 cm into the beaker from the outlet, the majority of the floes were 45 jam with a small portion approximately 70 /am. This was only 1/5 the size of the floes inside the Niskin bottle. The turbulence in the Niskin bottle created by four mixing propellers producing a G of 10 s'1 is comparable Conclusion These controlled experiments demonstrate that signif icant breakage of floes can occur when suspended material is withdrawn bom a Niskin bottle in the usual manner, either allowing the water to fall freely from the discharge valve at the bottom of the bottle or allowing the water to run gently down the inside wall of a beaker through a tube connected to the outlet valve of the Niskin bottle. Al ternative methods of obtaining samples from Niskin bottles for coagulation studies (such as using pipets through the top opening of the bottles) should be consid ered. Registry No. Water, 7732-18-5. Literature Cited (1) Berthois, L. Rev. Geogr. Phys. Geol. Dyn. 1961,1,39. (2) Biddle, P.; Miles, J. H. Sediment. Geol. 1972, 7,23. (3) Gibbs, R. J,; Konwar, L.; Terchunian, A Can. J. Fish. Aqat. Sd, 1983,40. (4) Kranck, K. Sedimentology 197$, 22, 111. (5) Ktanck, K. Sedimentology 1981, 28,107. (6) Krone, R. B. U.S, Army Corps Engineers Committee on Tidal Hydraulics Technical Bulletin, 1972, Vol. 19. (7) Owen, N. W International Association for Hydraulic Re search Congress, 1971, Vq L 4, 27. (8) Schubel, J. R.j Kana, T, W. Powder Technol. 1972,6,9. (9) Sheldon, R. W. Limnol. Oceanogr. 1968,13, 72. (10) Zabawa, C. Science (Washington, D.C.) 1978,202,49. (11) Gibbs, R. J,; Konwar, L. Environ,.ScL Technol. 1982,16, 119. (12) Gibbs, R. J. J. Sediment. Petrol. 1981, SI, 30. (13) Gibbs, R. J. J. Sediment. Petrol. 1982,52, 657. (14) Gibbs, R. J. Environ. Set. Technol, 1982,16, 298. (15) Niskin, S. Deep-Sea Res. 1962, 9, 501. TEH 0470001 CORRESPONDENCE Continent on "Development of an Air Quality Standard for Lead from Community Studies" SIR: Snee recently proposed a methodology to develop an air quality standard for lead bom community studies (1), The methodology can be summarized as follows: (a) specify the acceptable (distribution of) blood lead levels in the population (preferably the population at risk); (b) specify the air lead/blood lead relationship; (c) specify the (distribution of) blood lead (PbB) levels in the population at risk as it can be expected from nonair sources, using the air iead/blood lead relationship; (d) calculate the maximum amount of lead in the air that can be tolerated without violating the acceptable distribution of blood lead levels as specified under a. In my opinion, the methodology can only be used when a set of assumptions are made Shat Snee does not make explicit, and I will show that some of these assumptions are not very realistic. (a) Zielhuis has proposed an acceptable--not "desirable* as Snee mentions--distribution of PbB in 1974 (2). For young children, the population at the highest risk, this biological quality guide is not considered adequate any more (3,4), and much debate is still going on concerning the health risks of low-level lead exposure (5). This situ ation is not atypical in the environmental health field and can be handled by applying safety factors or margins of safety. Snee, however, seems to think that this is not necessary, as his methodology tacitly assumes that it is wise to bring blood lead levels only down to (or all the way up 0013-936X/83/0917-6376961.60/0 1983 American Chemical Society Environ. Scl. Technol., Vd. 17, No. 6, 1983 375  y '" > \ f,, ,.V, Environ. Sd. Tachnol. 1903, 17. 376-378 to) the upper limit of what is considered acceptable at a Thus, specifying a base line is a matter of choice--a certain moment in time. Essentially this is a policy pro choice as to what extent the high-risk subpopulations posal that can be (and should be) confronted with other within the population at risk are to be disregarded in the established environmental policy principles like "best process of setting a national air quality standard for lead. practicable means" etc. Registry No. Lead, 7439-92-1. fb) Snee has devoted much energy in specifying the air lead/blood lead relationship for both adults and children Literature Cited Id, 7). As his analyses appeared in other journals and are (1) Snee, R. D. Environ. Sci. Technot. 1982 16, 241-246. only referred to briefly in his recent contribution (1), I will only comment on them in a qualitative sense. There is one requirement that an air lead/blood lead relationship has to fulfill if one wants to use it in Snee's methodology, and that ib that one be absolutely sure that air lead varies independently of lead in other environmental pathways to men or that the air lead/blood lead relationship takes other environmental pathways into account when inde-. (2) Zielhuis, R. L. Tnt. Arch. Arbeitsmed. 1974,32,103-127. (3) Roels, H. A.; Buchet, J. P,; Lauwerys, R.; Buneaux, P.; Claeys-Thoreau, F.; Lafontaine, A.; Overschelde J. van; Verduyn, G. Environ. Res. 1978,15, 290-308. (4) Zielhuis, R. L.; Wibowo, A.A.E. Ned. Tijdschr. Geneeskd. 1978,122, 793-798. (5) Editorials: Brit. Med. J. 1982,284,529,1506; Lancet 1982, i, 1337*1338. (6) Snee, R. D. Int. Arch. Occup. Environ. Health 1981,48, pendent variation is not possible or likely. 219-242, For children, pathways like soil and dust have been shown to be as important or maybe even more important than air (8, 9). Lead is brought into the air by automobiles and other sources, and its concentration in air depends, among others, on source strength. Independent variation : (7) Snee, R. D. J. Air PoUut. Control Assoc. 1982,32,170-175. (ri) Duggan M J Water, Air, Soil PoOut 1980,14,309-1^1 (9) Sayre. J W: Chamey, E.; Vestal, J; Pless 1. B. Am J. Du Child. 1974,127,167-170. (10) Facchetti, S. Proc. Int. Conf. Manag. Contr. Heavy Met. Environ. (London) 1979,95-102. of lead in air is unlikely: where lead in the air is elevated, (11) Manton, W. I. Arch. Environ. Health 1977,32,149-159. lead in crops, soil, dust, etc., are or become elevated too. Thus, it is necessary to analyze the air lead concentration as an indicator of the combined environmental pathways. Snee does not mention this fundamental requirement, and it ib easy to show that his deduction of the air lead/blood (12) Rablnowitz, M. B.; Needleman, H. L. Science {Washington, D.C.) 1982,216, .1429-1431, (13) Oxley, G. R. Int. Arch. Occup. Environ. Health 1982,49, 341 -343. (14) Anouymus, Tweedc Kamer der Staten Generaal, 1981, 17371. lead slope for children from the Silver Valley lead study (15) Mahaffey, K, R.; Annest, 3, L.; Barbaric, H. E>; Murphy, (7) through the use of multiple regression models fails to R. S. Trace Subst. Environ. Health 1979,13, 37-60. meet this requirement The indicator approach would yield a slope dose to 3 rather than 1.0, and Snee's analysis (16) Quah, R. F.; Stark, A. D.; Meigs, J. W.; De Louise, E. R. Environ. -Health Perspect. 1982,44,169-164. of the data in fact simply confirmed once again that for children, air is not the most important environmental Bert Brunekreef pathway. Department of Environmental Health It is necessary to stress that the relationship between environmental lead and children's blood lead is a very complicated issue because of the many pathways and in Agricultural University 6709 BM Wagenlngen The Netherlands tervening variables that are involved. Quantitative rela tionships between the input of lead in the environment (e.g., through gasoline) and the resulting blood lead levels in children do not exist to date, and it will be difficult to derive them from community studies. An approach that seems to offer more perspective is the use of stable isotopes or stable isotope ratios. Unfortunately, few studies have followed this approach, and even fewer results are available (10,11). It is also unfortunate that Snee has failed to mention these studies with their inherent advantages over the traditional community studies. (c) The assumptions that have to he made here are largely the same as those concerning b. It is interesting to note that Snee uses rather old PbB data to derive his base line; these are only valid today when it is assumed that PbB values remain constant over time--which they obviously do hot as the general decline in both adult and child PbB values in different developed countries shows (12-14). Even more important than variations in time are probably variations between population gmupe of different regional or cultural background (IS, 16). The methodology assumes that something like a nationwide distribution of blood lead levels, related to nonair sources, can be estab lished. SIR: The quantitative determination of an air quality standard for lead is an important end complicated issue that has not been given adequate attention. Brunekreef accurately summarizes my proposed approach (1) and raises some important issues. I will discuss his concerns in the order in which he raised them. It will be apparent that I do not agree with some of his views. We must keep in mind at the outset that there are two key elements under discussion: the statistical metho dology used to develop the air quality standard and the data base used to derive the estimated distribution of blood lead values and the blood lead-air lead relationship used in the procedure. Changes in the latter require only a recomputation while disagreements over the former re quire a reformulation of the statistical model used. The proper formulation is critical because it can result only after we have an understanding of the system we are trying to regulate. (a) As I pointed out (I), the methodology I proposed will work for any "acceptable" (i.e., safe) level of blood lead. I chose the biological guideline proposed by Zielhuis (2), which calls for 50%, 90%, and 98% of the population at risk to have blood lead levels less than 20, 30, and 35 pg/dL, respectively. As I noted, the United States En The reality, of course, is that regional and cultural vironmental Protection Agency (EPA) guideline for differences will persist and that the environmental lead children of 99.5% of the population to have blood lead problem, e.g., the lead exposure problem, requires different levels less than 30 pg/dL (3) can also be used. Other forms of management for populations with different re guidelines may be appropriate. If the guideline distribu gional or cultural backgrounds. tion of blood lead levels changes in the future, then the TEH 0470002 I 376 Environ. SO. Tachnol., VpL 17, No, 6, 1983 0013-936X/83/0917-0376S01.60/0 1983 American Chemical Society DUP050082824 ' ":'ir . If ' vr:r<`!::v air quality standard will need to be reevaluated, j The question of safety factors is, for the most part, a J, societal (prlicy) judgment wtside the methodology used to calculate the standard. Margins of safety can be in corporated. It seems reasonable to assume, however, that any "acceptable'' blood lead level contains a margin of safetj As discussed later, the procedure described m ref 1 is conservative, thereby providing an additional mirgin ofsafety, because the distribution of true blood lead values is broadened by blood lead measurement error, plus any variation due to the inability to accurately measure an individual's air lead exposure. We must be careful in developing air quality standards to keep the scientific considerations separate from the societal (he., political) judgments. The calculations should be based on average valueE of the various inputs. Policy makers can promulgate a standard that is lower than the value calculated from the best available data and scientific knowledge if they feel that such action is necessary. If done in this manner, this action is clearly recognized as a societal judgment made outside of scientific considera tions. Incorporating societal judgments within the scien tific analysis (e g, the use of upper confidence limits rather than average values of model inputs) created confusion and reduces the effectiveness of the standard setting process because it is not dear to aU parties which decisions are based on scientific knowledge and which are based on societal judgments. The approach proposed in ref 1 is conservative because the distribution of observed blood lead values used contains measurement error that was not taken into account by the modeling procedure. It is a fundamental principal that an observed blood lead value for a given individual is equal tothe true blood leadlevel pirn measurement error blood lead values used to derive the standard. The distribution used is that for a population at a fixed air lead level. The spread in this distribution represents personto-person variation due to lead exposure from othe- sources as well as measurement error. In the Azar study (9), the inability to model the contribution to blood lead from parhwavs other than air shows up as variation in tht blood lead measurements around the fitted curve In the I epper-Levin study (10), lead exposure from other pathways also resulted in a larger within-group variation. In both of these instances, lead exposure from other pathways increases the variation in observed blood lead levels, thereby broadening the distribution. As noted earlier, a broader distribution produces lower values for the resulting air qualify Btandard, Lead exposure from soil and dust was incorporated in the air quality standard developed by the EPA (3). They assumed that at a zero air lead level, a child's blood lead level would average 12 jig/dL due to all sources of lead exposure except from the air. They then determined that an air lead level of 1.6 jig/m would result in a geometric mean Hood lead of 15 pg/dL, which is consistent with tile blood lead guideline of 30 pg/dL for the 99.6 percentile of the distribution. The EPA assumed that blood lead values follow a log-normal distribution with a geometric standard deviation of 1.3. In any study the inability to unbiaeedly sample each individual's air lead exposure also broadens the distribu tion of blood lead values at a fixed ah lead level. This is particularly true in stationary sampler studies Buch as that conducted by Tepper and Levin (10), in which a person's lead exposure is approximated by a single air sampler situated in the area in which the person lives or works. An extreme ease is population sampling studies such as due to sampling variation and analytical error: observed Hoodlead - true blood lead + measurement error. Blood the NHANES It study (11), in which air lead measure ments are not made. In these studies, the distribution of . lead measurement error, therefore, broadens the distri- observed Hood lead values contains variation due to dif | bution of observed blood lead values compared to the ferent air lead exposures as well as lead exposure from I distribution of true values (4). This produces a lower air other pathways. The variation in the NHANES II study, ' quality standard than would occur if the standard were due to the 64 sampling locations, as well as any time trends computed on a true value basis by taking the measurement that occurred during the 4-year study (1976-1980), further error into account. Lucas (4) found that 50% or more of the total variation in blood lead measurements can be due broadens the observed blood lead distributions. The use of distributions such as those developed iq the NHANES to measurement error. Statistical procedures to properly account for measurement error are discussed by Lucas {4) II study will result in a conservative air leqd standard due to the broader distribution of blood lead levels. and Hahn (5). These techniques can be used to further Brunekreef states, without documentation or reference refine the methodology described in ref 1. to other papers, that the blood kad-rair lead slope is greater (b) Brunekreef properly points out that it is necessary to take all sources of lead exposure into account when setting an air qualify standard and notes that soil and dust than 1 and may be as large as 3. The basis for this con jecture is unclear, for an exhaustive study of the literature shows slopes ranging from approximately 1 to 2 with an aro important sources of lead for children. Lead exposure overall average value between 1.0 and 1.4 (12). The de !from sources other than the air is an integral part of my termination of the appropriate slope is critical to the de proposed procedure (1) and that used by the EPA (3). termination of the standard. It is, however, an input to Improvements are needed in Ibis regard and should be my proposed methodology and is independent of the I incorporated as hew data oh the other pathways becmomeethodology. The standard could be derived by using a s available. variety of slopes if appropriate. ( Lead in dust and dirt comes from many sources in (c) I do not share Brunekreefs concern about the age cluding house paint, soil lead, previous air lead levels, and of the data base used in my calculations. The studies of g current air lead levels. The linear correlation coefficient Azar et al. and Tepper and Levin (9,10) are, today, gen | between air lead and soil and dust lead is not large, how- erally considered to be the best available prospective ep I ever, being in general less than 0.5 (6, 7) and sometimes idemiologic studies of the relationship between blood lead dose to zero (8). Quantitative modeling of these rela- and air lead. The critical items are the distribution of | tionships is an important area for farther research, but the observed blood lead levels, as estimated by the Tepper and I data available do not suggest a correlation strong enough Levin (10) study, and the blood lead-air lead relationship, i to justify the use of air Had as an indicator variable as asestimatedby theAzaretah study (9,13) andbyalinear suggested by Brunekreef. model with a slope of 1. These inputs to the air qualify In my procedure (I) lead exposure from nonair lead sources is accounted for by the distribution of observed lation. Blood lead levels in the general population are Environ. 8ci. Technol., Vol. 17, No. 6,1983 377 DUP050082825 TEH 0470003 j t ---. J 4 lower now then they were when these two studies were conducted for severed reasons, including the decrease in the lead content of our food and water supply, the re duction in the number of houses with leaded paint, and the declining use of lead in gasoline. These changes should have no effect on the relationship between blood lead and air lead and can only lessen the spread of the withlnpopulation distribution. !t is certainly appropriate to reevaluate the standard in the future and redo the calcu lations as new data become available, suggesting that such calculations axe appropriate. Brunekreef also raises concerns about the effects of variations in population groups. Contrary to his statement, the methodology assumes a distribution for the population at higher risk and not a nationwide distribution. It should also be recognized that differences present in the popu lation due to culture, sex, race, etc., will broaden the dis tribution of Observed blood lead levels. Lead exposure problems may require different forms of management for different populations; however, there is only one air quality standard. The base line will be determined by the regu latory agencies and is an input to the methodology de scribed in ref 1. Registry No. Lead, 7439-92-1. Literature Cited (1) Snee, R. D. Environ. Sci. Technol. 1982, 16,241-246. (2) Zielhuis.R. L, Int. Arh..Arbeitsmed. 1974,32,193-127. (3) U.S. EPA, Fed. Regist. 1978,43, No. 194. (4) Lucas, J. M. Am. Jnd. Hyg. Assoc. J. 1981, 42, 88-96. (5) Hahn, G. 3, J. Quel. Technol. 1982,14,117-121. (6) Yankel, A. J.; von Lindera; L H.; Walter, S. D. J. Air Pollut. Control Assoc, 1977, 27,763-767. (7) Angle, C. R.; Mclntire, M. S. J. Toxicol. Environ. Health. 1979,3, 868-670. (8) Stark, A. D.; Quah, R. T.; Meigs, J. T.; DeLouise, E. R. Environ. Res. 1982,27, 372-383. (9) Azar, A.; Snee, R. D.; Habibi, K. Environ, Quat, Saf. 1976, 2, 264-290. (10) Tepper, L. B.; Levin, L. S. Environ. Qual. Saf. 1975,2, 162-197. (11) Mahaffey, K. R.; Annest, J. L-; Roberta, J.; Murphy, R. S. New England J. Med, 1982, $07,647-617. (12) Snee, R. D. Int. Arch. Occup. Environ. Health 1981,48, 210-242. (13) Snee, R. D.Jnt. Arch. Occup. Environ. Health 1982,50, 303-319 Engineering Department E. I. du Pont de Nemours and Co. Inc. Wilmington, Delaware 10898 RonaldDSnee 379 Environ. Sri. technol., Vri. 17, No. 6. 1983 TEH 0470004 DUP050082826