Environ. Sei. Technol. 1984, 18, 287-291
(11) Pitts, J. N.; Winer, A. M.; Darnall, K. R. "Chemical Consequences of Air Quality Standards and of Control Implementation Programs: Roles of Hydrocarbons, Oxides of Nitrogen, and Aged Smog in the Production of Photochemical Oxidant", final report to the California Air Resources Board under Contract 4-212, 1976, pp 1-444. (12) Graedel, T. E. J . Phys. Chem. 1977,81, 2312-2314.
(13) Jeffries, H. E., personal communication. (14) Whitten, G. Z., personal communication.
Received for review May 2,1983. Accepted October 3,1983. This work was supported by the State of California Air Resources Board Agreement A2-042-32.
Summertime Variations in Polycyclic Aromatic Hydrocarbons at Four Sites in New Jersey Ronald Harkov Office of Science and Research, New Jersey Department of Environmental Protection, Trenton, New Jersey 08625
Arthur Greenberg and Faye Darack Department of Chemical Engineering and Chemistry, New Jersey Institute of Technology, Newark, New Jersey 07102
Joan M. Daisey and Paul J. Lioy" Institute of Environmental Medicine, New York University Medical Center, Tuxedo, New York 10987
Variations in the summertime concentrations of selected polycyclic aromatic hydrocarbons (PAH) collected by using inhalable particulate samplers (IPM-D, < 15 pm) at four sites in New Jersey are presented and examined. The levels of PAH found in this study are consistent with other urban values reported in the literature. While day-to-day trends in PAH concentrations at the four sites were influenced by regional meteorology, it appears that local sources had the greatest influence on ambient levels. Comparison of selected PAH with IPM, EOM (extractable organic matter), and Sod2values at each site showed weak correlations. However, intersite and intrasite Spearman rank correlations among PAH were significant and suggest a common type of source emitter at the urban locations during the summer. The intersite correlations also reflect the proximity of the four sites. Introduction Polycyclic aromatic hydrocarbons (PAH) are components of the organic aerosol which have both mutagenic and carcinogenic properties (1). These pollutants have been measured in ambient air for over 20 years, yet the majority of these studies have only focused on the potent animal carcinogen benzo[a]pyrene. Most recent studies of PAH have been concerned with the determination of average concentrations without regard to daily or seasonal variations in atmospheric levels (2-5). In addition, some limited research has been directed toward identifying PAH sources (6-8). The present study, however, is directed toward careful analysis of the daily and seasonal variations of PAH concentrations, meteorological influences, relative concentration of selected PAH (i.e., PAH profiles), and correlations with other pollutants as well as measures of biological activity. The latter point will be the subject of another paper on the Ames mutagenicity assay of these samples. The aim is to contribute to the understanding of the environmental significance of this class of compounds. The PAH study detailed here is a part of the New Jersey Airborne Trace Element and Organic Substance (ATEOS) program which has been described elsewhere (9-11). In the present paper, results are reported from the summer of 1981 field campaign. The daily variability between and 0013-936X/84/0918-0287$01.50/0
within sampling locales and relationships between documented meteorological events and source types are analyzed and discussed. Experimental Section Sampling. The sampling protocols and site descriptions for the ATEOS program have been described in detail elsewhere (9-11) and will only be briefly outlined. A General Metal Works size-selective inlet (DE0< 15 pm) high volume sampler (40 CFM) was used to collect ambient aerosol in preignited Gelman-AE fiberglass filters. IPM samples were collected simultaneously by a colocated size-selective inlet sampler which used Spectrograde filters, thus allowing for analysis of additional pollutants. Twenty-four hour sampling occurred from 10 a.m.-10 a.m. 7 days per week at three urban sites (Camden, Elizabeth, and Newark) and one rural background site (Ringwood) for the 6-week period from July 6,1981, to August 14,1981. The four sites are shown on a map of New Jersey (Figure 1). The Newark site, in northeastern New Jersey, is at the interface of a highly industrialized area and a stable residential community; petrochemical, inorganic chemical, leather tanning, truck and auto painting, and precious metal recovery and refining facilities are located within 1 km of the site. Refineries and petrochemical and commercial areas are near the Elizabeth site which is about 8 km from the Newark site and within a residential community. The Camden site, in the southwest part of the state, is heavily influenced by a variety of industries located along the Delaware River to the west as well as by the Philadelphia airshed. Ringwood State Park is located in the extreme northeast of New Jersey, some 60 km from Newark. Analysis. A complete description of the analytical procedure is found elsewhere (10) and can be outlined as follows. Airborne particulate matter collected on filters was subjected to sequential Soxhlet extraction with cyclohexane (CX), dichloromethane (DCM), and acetone (ACE), and each fraction was subjected to rotoevaporation and nitrogen gas blow down. The CX fraction was utilized for PAH analysis. (Very small amounts of PAH remain in the DCM fraction relative to the preceding CX fraction.)
0 1984 American Chemical Society
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287
Table I. Geometric Mean Concentrations ( M G )of Selected Polycyclic Aromatic Hydrocarbons (PAH) at Four Sites in New Jersey during the Summer of 1981 ATEOS Program Newark
__
benzo[a]pyrene (BaP) benzo[e]pyrene (BeP) benzo[j]fluoranthene (BjF) benzo[ k lfluoranthene (BkF) benzo[b Ifluoranthene (BbF) indeno[ 1,2,3-cd]pyrene (IcdP) benzo [ g h i Iperylene (BghiP) coronene (Cor) perylene (Per) dibenz[ac ]anthracene (DBacA)
Elizabeth
Cam den
--___
na
MGb
71
MG
71
MG
33 37 37 28 30 29 36 36 27 36
0.23
28 34 33 22 23 27 33 33 22 29
0.14 0.13 0.09 0.14 0.20 0.26 0.41 0.35 0.04 0.03
29 37 37 33 30 27 35 35 23 32
0.20 0.14 0.13 0.15 0.27 0.34 0.35 0.29 0.06 0.03
0.18 0.16 0.20 0.27 0.46 0.56 0.47 0.10 0.03
Ringwood I2
11 11 10
8 10 12 10 9 9 9
lVG
0.06 0.03 0.06 0.03 0.06 0.09 0.09 0.08 0.03 0.09
a Number of resolvable samples, M G = geometric mean concentration in ng/m3. Values for 7/21-22 in Newark (ng/m3): BaP, 8.74;BeP, 6.12;BjF, 6.50;EkF, 7.97;BbF, 11.16;IcdP, 16.36;BghiP, 9.52;Cor, not resolvable;Per, 3.29; DBacA. 0.88.
N E W YORK CONNECTICUT I
Flgure 1. Site locations used in the ATEOS project and nearby reference urban areas.
These steps were followed by addition of an internal standard, 1-methyltrypticene, and separation of the PAH class from other CX-soluble organics using thin-layer chromatography (TLC) on silica gel G plates (fluorescent coated). The plates were developed with n-hexane-toluene, 1:l. Tetrahydrofuran washing of the scraped TLC adsorbent was followed by concentration under nitrogen to about 0.1 mL and injection of 10-20 pL into a highperformance liquid chromatography (HPLC) apparatus operated in the reverse-phase mode using Perkin-Elmer PAH/10 and Separations Group Vydac columns with elution by aqueous acetonitrile (10). Eluting compounds were monitored simultaneously by UV absorbances at 280 and 365 nm as well as fluorescence (360-nm excitation, >440-nm emission). Data Assurance. All sampling and analyses in the ATEOS program are subject to a rigorous quality assurance and quality control (qa/qc) plan as described in a previous report (10). The qa/qc for PAH includes comparison with NBS standards, interlaboratory comparisons, internal standards, spikes, blanks, Beer’s law plots, daily 288
Environ. Sci. Technol., Vol. 18, No. 4, 1984
standardization of instruments, and comparison of 280/365 nm UV ratios and UV/fluorescence ratios of the samples to those of standards. In those instances in which the identity of a compound could not be confirmed by these ratios, the compounds’s concentration was omitted from the data set. Results The 6-week geometric means for 10 PAH compounds measured during the summer of 1981 ATEOS campaign are shown in Table I. Due to the low concentrations of particulate organic matter found at the Ringwood site, this data set represents 3-day composites. Generally, Newark exhibited the highest PAH values, with Camden and Elizabeth being very similar and Ringwood having considerably lower values. Figure 2 shows the daily variation in concentration for benzo[a]pyrene at all four sites during the campaign. Lioy et al. (12)have shown in a previous analysis that there were three episodes of regional photochemical smog, which were ozone, and EOM (excharacterized by high IPM, Sod2-, tractable organic matter) levels. Although the levels of six selected PAH [benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), coronene (Cor), benzo[ghi]perylene (BghiP), indeno [1,2,3-cd]pyrene(IcdP), and benzop]fluoranthene (BjF)] were also higher during episode (EP) than in nonepisode (NEP) periods (Table 11),no strong relationship was noted with the above pollutants (Le., R,, C 0.6, p > 0.01; R,, = Spearman correlation coefficients). These six PAH compounds were chosen because they include the most complete data set during these time periods. Values of R,, > 0.7 were only found for BaP and BjF vs. cyclohexanesoluble organics (CX) at the Newark site. It is clear that the selected PAH concentrations can vary significantly according to the influence of specific source emitters at each site. For example, the extremely high levels in Newark on July 21-22 were not found in Ringwood or Camden. Unfortunately, the Elizabeth sample for that date could not be resolved by HPLC analysis. However, less localized pollution patterns can also be discerned through statistical analysis. For example, when intersite comparisons were made between the Newark and Elizabeth sites (only 8 km apart), Spearman correlation coefficients for the six selected PAH were greater than 0.6 and highly significant (p C 0,001; Table 111). In contrast,the correlations for PAH concentrations at these two northern New Jersey urban sites with those at the southern urban site, Camden, over 100 km distant, are much poorer (Table 111). It is also noteworthy that while the geometric means for PAH were generally 50-8070 higher for EP than NEP
7/6
1/r 8
7/12
7/24
ah
7/30
&/I 1
OATE
Flgure 2. Daily concentrations of BaP measured at all ATEOS study sites during the 1981 summer study.
Table 11. Geometric Mean Concentrations ( M G )of Six PAH a t the Three Urban Sites in Nonepisode Periods (NEP) and Episode Periods (EP) during the Summer of 1981 Newark
Elizabeth
NEP
BaP BeP BjF BghiP IcdP Cor
EP
NEP
Camden EP
NEP
EP
na
~ , b
n
MG
n
MG
n
MG
n
MG
n
J@G
24 25 25 26 20 26'
0.21 0.17 0.14 0.48 0.55 0.20
9 12 12 10 9 10
0.33 0.20 0.23 0.81 0.89 0.43
20 25 25 23 17 24
0.12 0.11 0.09 0.39 0.30 0.18
8 9 9 10 10 9
0.22 0.25 0.11 0.52 0.57 0.30
21 25 25 23 16 34
0.23 0.14 0.12 0.32 0.44 0.17
8 12 12 12 11 11
0.22 0.16 0.15 0.43 0.46 0.19
a n = number of resolvable samples. footnote b of Table I.
Concentrations are reported in ng/m3.
N o data point for 7/21-22 day; see
Table 111. Intersite Spearman Rank Correlations (R,) for Six PAH and Cyclohexane-Soluble Organics (CX) Elizabeth/Newark Camden/Newark Camden/Elizabeth a
BaP
BeP
BjF
IcdP
BhgiP
0.76' 0.29 0.03
0.63' 0.52 0.37
0.6 2' 0.26 0.18
0.84' 0.51 0.44
0.63' 0.37 0.37
Cor
cx
0.75' 0.52 0.45
0.83' 0.39 0.45
Significant a t p < 0.001.
at the Newark and Elizabeth sites, the corresponding increase at Camden is generally less than 25% (Table 11). This parallels the findings for EP/NEP comparisons of EOM (10) at the urban sites in which Newark and Elizabeth levels increased by 70-100% at Newark and Elizabeth and only 4 M O % at Camden. Spearman rank correlations for the selected PAH within each of the urban sites reveal R,, > 0.70 that were significant at the p < 0.001 level, indicating that similar types of PAH sources were present near each site. The PAH compound distributions (or profiles), shown in Figure 3, were also similar.
Discussion The levels of PAH reported here are similar to those found in other U.S. urban areas in the summer (1)and at a number of monitoring sites in New Jersey during 1979 (13). Sumertime PAH levels tend to be at a minimum, reflecting changes in prevailing meteorology and a lack of a major PAH source, residential fossil fuel combustion for heating ( I ) . While one would also anticipate greater photochemical and chemical decomposition (e.g., with ozone) during the summer period, the similarities between relative proportions of different PAH (i.e., PAH profiles)
when summer and winter samples are compared are strong (13). Clearly, more research is needed in this area in order to understand ambient PAH profiles in terms of sources and atmospheric decomposition pathways. The major PAH source during the summer in New Jersey is most likely motor vehicle emissions, an area source, although specific point sources may have a disproportionately large impact on ambient concentrations on individual days at each of the urban sites. An analysis of the information from the summer of 1981 campaign indicates the importance of motor vehicle emission contributions to ambient PAH levels. The daily variations in concentration of the PAH are similar for the Newark and Elizabeth sites even though the point sources in these two areas differ (e.g., see BaP in Figure 2). Source commonality is supported by similarities in PAH profiles measured at each site (Figure 3). It should again be noted that site proximity for Newark and Elizabeth strengthens the observed correlation. It must also be noted that New Jersey has the highest motor vehicle density in the United States and that motor vehicles are major sources for a large number of organic air pollutants (14-16). A comparison of the ratios of five selected PAH (BeP, BjF, IcdP, BghiP, Envlron. Sci. Technol., Vol. 18, No. 4, 1984
289
Table IV. ( A ) Ratios of Selected PAH to BaP from Summer of 1951 ATEOS Campaign during Nonepisode Periods (NEP) and Episode Periods (EP) and (B) PAK:BaP Ratios Derived from Tunnel and Exhaust Data ( A ) Ambient Studies
Newark 0
.
NEP r - - 1
t
c 0
0.4
0.2
BaP BeP BjF IcdP BghiP Cor
I
I
i
Jl
0
Flgure 3. Histogram of arithmatic mean concentrations of selected PAH measured at all ATEOS study sites during the 1981 summer study.
and Cor) to BaP, to source emissions data from the literature ( 4 , 14, 17-19), is appropriate for analyzing the impact of automotive emissions on New Jersey (Table IV). A number of observations can be made from this comparison. The PAH:BaP ratios change only slightly at the urban and rural sites for summertime episodic (EP) and nonepisodic (NEP) periods, with the greatest difference occurring at the Newark site. Since BghiP and Cor levels are indicative of motor vehicle contributions to ambient PAH levels, the ratios of these two compounds to BaP can be used as indicators of the relative contribution of this source to atmospheric PAH concentrations in New Jersey during the summer of 1981. Both tunnel and automobile exhaust studies (Table IV) have produced a number of different Cor:BaP and BghiP:BaP ratios. These ratios differ between studies due to differences in sampling and analytical methods, in sampling season, and, in the case of tunnels, in motor vehicle composition and exhaust circulation rates, For the purposes of this report, ratios of Cor:BaP = 2.5 and BghiP:BaP = 2.3 are adopted from recent studies in the Lincoln and Holland Tunnels (18) which connect New York City and northeastern New Jersey. Tunnel and exhaust condensate ratios are presented in Table IV for comparison. The ratios from the tunnel samples are more appropriate for comparison for two reasons: first, the analytical procedures are identical; second, the motor vehicle composition in the tunnels should be similar to the traffic composition at the urban New Jersey sites. On the basis of the ratios, it appears that the Elizabeth site is affected primarily by motor vehicle emissions during EP as well as NEP. In contrast, Newark seems to be influenced by motor vehicles during NEP, but additional sources are important during EP. These observations are not surprising considering that these two sites are only 8 km apart and contain a high density of motor vehicles. However, the presence of other PAH 290
Environ. Sci. Technol., Vol. 18, No. 4, 1984
Camden
Ringwood
EPa NEP
EP
NEP
EP
NEP
EP
1.0 0.6 0.7 1.7 2.2 1.8
1.0
1.0 0.7 0.6 1.8 1.7 1.6
1.0 0.7 0.7 1.5 1.7 1.3
1.0 3.6 0.8 1.0 1.2 0.8
1.0 0.5 0.7 1.8 1.2 1.8
1.0 0.8 0.6 1.8 2.8 2.4
1.0 0.7 2.2 2.4 2.3
(B) Tunnel and Exhaust Studies
I
1
1.0 0.9 0.7 2.3 3.0 2.4
Elizabeth
Grimmer e t al. ( 1 7) Kebbekus e t al. ( 1 8 ) Handa et al. ( 4 ) Lee et al. ( 19) Grimmer (14) a
Cor:BaP
BghiP:BaP
1.6 2.5
2.3 2.3 2.8
1.6 2.5
4.0
sample type tunnel tunnel tunnel exhaust exhaust
Newark values d o not include 7/21-22 data.
sources in the area of the Newark site can be deduced from selected PAHBaP ratios observed on 7\21-7122 (see Table I). On that day, the PAH levels were virtually as high as the sum of all the other campaign days. Specifically, the 1cdP:BaP and BghiP:BaP ratios (1.3 and 1.1,respectively) were considerably lower than the NEP ratios (2.3 and 3.0, respectively). The poor correlations of the selected PAH with IPM, SO4*-, and ozone found in this study are not surprising considering that PAH are primary pollutants and, during the summer season, S042- and ozone are secondary contaminants and will be a combination of some locally produced and transported material. Both S042- and acetone-soluble matter are the two components that have been determined to dominate daily IPM variability in New Jersey during the summer (11). Acetone-soluble matter and 50:- make up nearly 50% of the IPM and together furnish the most likely explanation of the weak correlations between IPM and PAH. Only the CX fraction shows any significant correlation with PAH, and this correlation is strongest for the Newark site. Since the above arguments indicate that there are non-motor vehicle sources at the Newark site, one must anticipate the presence of industrial sources emitting both CX and PAH. A potential sourcecategory for the PAH at the Newark site is secondarynonferrous metal smelters. This point finds some support in the data analysis since the CX fraction was significantly correlated (RSp> 0.70, p g 0.001) with Pb, Cu, Fe, Ni, and Zn. However, more summer samples and wind rose analyses will be necessary to evaluate the significance of this source type. Conclusions The daily levels of selected airborne particulate PAH in New Jersey during the summer of 1981 are presented. Spearman rank correlation coefficients were significant for six selected PAH for certain intersite as well as intrasite comparisons, These results, along with selected PAH:BaP ratios and correlations with Pb, indicate that motor vehicle traffic was the major PAH source during the summer. The influence of additional non-motor vehicle PAH sources is apparent at the Newark site, and their influence was particularly significant on July 21-22, when PAH levels were virtually equal to the other sampling days combined.
Environ. Sci. Technol. 1984, 18, 291-294
This serves to reemphasize the well-known limitations in occasional, as opposed to daily, sampling.
(11)
Acknowledgments We thank all the those members of the ATEOS program who have run sites and completed sample analyses and data analysis. We also thank Thomas Burke, Director of Science and Research of the New Jersey Department of Environmental Protection, for his continuing encouragement on this project.
(12) (13)
(14)
Literature Cited (1) Santodonato, J.; Howard, P.; Basu, D. J. Environ. Pathol. Toxicol. 1981, 3, 1-364. (2) Faoro, R. B.; Manning, J. A. J. Air Pollut. Control Assoc. 1981, 31, 62-64. (3) Katz, M.; Chan, C. Enuiron. Sci. Technol. 1980,14,83%843. (4) Handa, T.; Kato, Y.; Yanamura, T.; Ishii, T., Environ. Sci. Technol. 1980,14,416-422. (5) Butler, J. D.; Crossby, P. Sci. Total Enuiron. 1979,11,53-58. (6) Daisey, J. M.; Leyko, M. A.; Kneip, T. J. “Polycyclic Aromatic Hydrocarbons”; Jones, P. W.; Leber, P., Eds.; Ann Arbor Press: Ann Arbor, MI, 1979; pp 201-215. (7) Daisey, J. M.; Lioy, P. J. J. Air. Pollut. Control Assoc. 1981, 31, 567-569. (8) Greenberg, A.; Bozzelli, J. W.; Cannova, F.; Forstner, E.; Giorgio, P.; Stout, D.; Yokoyama, R. Environ. Sci. Technol. 1981, 31, 567-569. (9) Harkov, R.; Fischer, R. R o c . Annu. APCA Conf.,75th 1982, 1-20 (Paper 82-1.1). (10) Lioy, P. J.; Daisey, J. M.; Greenberg, A.; Bozzelli, J.; Kebbekus, B.; McGarrity, G. ”First Annual Report of the
(15) (16) (17) (18) (19)
ATEOS Program”; New Jersey Department of Environmental Protection: Trenton, NJ, 1982; pp 1-270. Lioy, P. J.; Daisey, J. M.; Atherholt, T.; Bozzelli, J.; Darack, F.; Fischer, R.; Greenberg, A,; Harkov, R.; Kebbekus, B.; Kneip, T. J.; Louis, J.; McGarrity, G.; McGeorge, L.; Reiss, N. M. J. Air Pollut. Control Assoc. 1983, 33, 649-657. Lioy, P. J.; Daisey, J. M. Reiss, N. M.; Harkov, R. Atmos. Environ. 1983, 17, 2321-2330. Bozzelli, J. W.; Kebbekus, B. B.; Greenberg, A. “Analysis of Selected Toxic and Carcinogenic Substance in Ambient Air in New Jersey”; New Jersey Department of Environmental Protection: Trenton, NJ, 1980. Grimmer, G. “Analysis of Automobile Exhaust Condensates in Air Pollution and Cancer in Man”, 1977, IARC Publication No. 16. Hampton, C. V.; Pierson, W. R.; Harvey, T. M.; Updegrave, W. S.; Marano, R. S. Environ. Sci. Technol. 1982, 16, 287-298. Hampton, C. V.; Pierson, W. R.; Schuetzle, D.; Harvey, T. M. submitted for publication in Enuiron. Sci. Technol. Grimmer, G.; Naujack, K. W.; Schneider, D. ”Polynuclear Aromatic Hydrocarbons”; Bjorseth, A.; Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1980; pp 107-125. Kebbekus, B. B.; Greenberg, A.; Bozzelli, J. W.; Darack, F.; Eveleens, C.; Horgan, L.; Strangeland, L. J. Air Pollut. Control Assoc. 1983, 33, 328-330. Lee, F. S. C.; Prater, T. J.; Ferris, F. Polynuclear Aromatic Hydrocarbons,Jones, P. W.; Leber, P., Eds.; Ann Arbor Press: Ann Arbor, MI, 1979; pp 83-110.
Received for review July 21,1983. Accepted October 3,1983. This research is sponsored by the New Jersey Department of Environmental Protection, Trenton, NJ.
NOTES Butyltin Compounds and Inorganic Tin in Sediments in Ontario R. James Magulre Environmental Contaminants Division, National Water Research Institute, Department of the Environment, Canada Centre for Inland Waters, Burlington, Ontario, Canada L7R 4A6
w A method has been developed for the analysis of butyltin species and inorganic tin in sediments, and the presence of these compounds in sediments in Ontario is reported for the first time. Although inorganic tin occurred frequently in sediments collected around the province, butyltin species were found mainly in the sediments of harbors, reflecting earlier findings on their occurrence in water, with which these findings are compared. Tri-nbutyltin, the most toxic of the butyltin species to aquatic life, was present at 0.5 mg/kg (dry weight) in the top 2 cm of sediment in Toronto Harbour. In addition, tri-n-butylmethyltin and di-n-butyldimethyltin were found in the sediment of a few harbors, indicating that some butyltin species can be methylated in aquatic environments. Introduction Organotin compounds are used in three main ways, viz., as stabilizers for polyvinyl chloride, as catalysts, and as biocides (1). The increasing annual use of organotin 0013-936X/84/0918-0291$01.50/0
compounds raises the possibility of environmental pollution. Organotin compounds are a class of compounds about which more information is sought under Canada’s Environmental Contaminants Act (2) regarding toxicology and environmental fate. Recently we reported the occurrence of butyltin species and inorganic tin in water at 30 locations in Ontario (3);this article reports a method for the analysis of butyltin species and inorganic tin in sediments and the concentrations of these compounds in sediments collected at the same time as the aforementioned water samples. Experimental Methods Materials. Bis(tri-n-butyltin) oxide (97%), di-n-butyltin dichloride (96.5%),n-butyltin trichloride (95%),tin (99.9%), and 2 M n-pentylmagnesium bromide in diethyl ether were from Ventron (Danvers, MA) (three different lots of n-pentylmagnesium bromide purchased after this work was completed were found to contain unacceptably high concentrations of the four butylpentyltin compounds,
Published 1984 by the American Chemical Society Environ. Sci. Technol., Vol. 18, No. 4, 1984 291
