Interstudy and Intrastudy Temporal Trends of Polychlorinated Biphenyl

Apr 1, 2014 - ... two studies with halving times of 3–6 years; the concentrations of PAHs and ... aromatic hydrocarbons over the southeastern Tibeta...
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Letter pubs.acs.org/journal/estlcu

Interstudy and Intrastudy Temporal Trends of Polychlorinated Biphenyl, Pesticide, and Polycyclic Aromatic Hydrocarbon Concentrations in Air and Precipitation at a Rural Site in Ontario Liang-Ying Liu, Amina Salamova, and Ronald A. Hites* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, United States S Supporting Information *

ABSTRACT: Polychlorinated biphenyl (PCB), organochlorine pesticide, and polycyclic aromatic hydrocarbon (PAH) concentrations were measured in air (in the vapor and particle phases) and in precipitation samples collected at Point Petre on the northeastern shore of Lake Ontario as a part of the Integrated Atmospheric Deposition Network. These data were measured in two separate studies, one running from 1992 to 2003 (inclusive) and the other from 1998 to 2011 (inclusive). Having these two independent studies is a direct way of measuring changes in atmospheric concentrations and comparing interstudy changes to intrastudy changes. The concentrations of almost all pesticides declined between the two studies with halving times of 3−6 years; the concentrations of PAHs and PCBs did not change much between the two studies. This suggests that there are continuing sources of PAHs and PCBs to the Great Lakes atmosphere. PAH concentrations were elevated in the winter when space heating consumes greater amounts of fuel and emits larger amounts of PAHs. Pesticide and PCB concentrations were elevated in the summer because of enhanced volatilization from terrestrial or aquatic surfaces during hot summer days. Although there were a few exceptions (notably lindane), in general, the data from the two study periods gave similar results.

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INTRODUCTION To determine the effectiveness of regulations, many nations have initiated programs for investigating the temporal trends of persistent organic pollutants (POPs) by measuring their concentrations in various environmental media as a function of time.1,2 These pollutants include many chlorinated pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Some of these compounds, notably, DDT and PCBs, have been banned for several decades, but others, such as PAHs, are the byproducts of the combustion of organic fuels and continue to be released around the globe.3 One example of a program designed to determine the temporal trends of POPs in the atmosphere is the Integrated Atmospheric Deposition Network (IADN), a joint Canadian− United States monitoring and research program. This program has been in continuous operation since 1991, and it has measured the concentrations of various contaminants (such as PCBs, organochlorine pesticides, and PAHs) in air (in the vapor and particle phases) and in precipitation at several sites near the Great Lakes every 12−24 days. In fact, time trends of those contaminants in air and precipitation have been reported in several studies,4−11 and it is encouraging to know that the concentrations for many of these atmospheric contaminants around the Great Lakes are decreasing. Point Petre is the easternmost IADN site and is located on the northeastern shore of Lake Ontario. It is the only IADN site at which samples are taken simultaneously by both the Canadian and U.S. teams. Both the Canadian and U.S. © 2014 American Chemical Society

laboratories have measured the same set of compounds at this site, but there are many differences in the details. The published Canadian measurements covered the period from 1992 to 2003 (inclusive);4−8,10 the U.S. measurements covered the period from 1998 to 2011 (inclusive). The samples were collected for 24 h every 12 days in the former study but for 24 h every 24 days in the latter study. Particle-phase pesticides were measured in the latter study but not in the former. The time trend analysis method used for the former study did not allow for the calculation of dates on which the concentrations of the pollutants were maximal in the vapor phase, but the latter study did. In addition to these sampling and data reduction differences, there were also some differences in the analytical methods used for the two studies. For example, PAHs were quantitated by liquid chromatographic fluorescence in the former study but by gas chromatographic mass spectrometry in the latter. In fact, the Point Petre site was originally established as an intercomparison site, where samples were collected simultaneously with different sampling equipment and subsequently analyzed by different analytical methods. Results of these intercomparison experiments have been published previously,12 and these results show that the two sampling and Received: Revised: Accepted: Published: 226

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Table 1. Concentrations, Halving Times, and Maximal Concentration Dates for Four Representative Compounds or Compound Groups Measured in the Atmosphere at Point Petre, Ontarioa γ-HCH

concn (pg/m3 or pg/L) t value halving time (years) t value maximal date t value

endosulfan I

vapor

particle

precipitation

vapor

particle

precipitation

(1992−2003)6

(−)

(1997−2003)5

(1992−2003)6

(−)

(1997−2003)5

(1999−2011)

(1998−2011)

(1998−2003)

(2000−2011)

(1998−2003)

(2000−2011)

12 ± 0.7 6.6 ± 0.9 −4.7

− 1.2 ± 0.2 −

1400 ± 170 320 ± 41 −6.2

110 ± 22 50 ± 7.6 −2.6

− 8.6 ± 1.6 −

600 ± 93 640 ± 68 ns

7.8 ± 0.7 4.0 ± 0.3 −5.0

− 2.1 ± 0.5 −

2.5 ± 0.3 2.8 ± 0.2 ns

8.2 ± 1.4 ns −

− 2.0 ± 0.3 −

5.3 ± 2.0 7.4 ± 1.2 ns

− July 14 ± 4 −

− ns −

ns May 8 ± 7 −

− July 23 ± 3 −

− April 26 ± 15 − ΣPCB

June 17 ± 8 June 4 ± 5 ns

ΣPAH vapor

particle

precipitation

vapor

particle

precipitation

(1997−2003)7

(1997−2003)7

(1997−2003)4

(1992−2003)8

(−)

(1992−1996)10

(2000−2011)

(1999−2011)

(−)

(1998−2011) concn (pg/m3 or pg/L) t value halving time (years) t value maximal date t value

(1998−2011)

(2000−2011)

1300 ± 55 1700 ± 91 3.8

710 ± 71 470 ± 35 −3.0

76000 ± 8000 67700 ± 5900 ns

80 ± 2.6 90 ± 5.7 ns

− − −

− 780 ± 50 −

ns 12 ± 2.3 −

6.7 ± 1.6 11 ± 3.1 ns

ns 11 ± 2.8 −

7.1 ± 0.4 9.3 ± 1.3 ns

− − −

− 12 ± 3.1 −

− November 15 ± 25 −

January 27 ± 5 ns −

January 22 ± 6 January 19 ± 5 ns

− July 17 ± 4.2 −

− − −

− March 4 ± 13 −

a

In each set of data, the top number is from published studies8−12 and the middle number is from this work. The bottom number is the t value, which indicates if the difference between the former and latter studies is statistically significant (ns means nonsignificant). In all cases, the errors are standard errors. PCB data reported in a previous study from our laboratory10 were not used here because the PCB congener list was not specified in the 1992−2003 study.

For the later data, samples were collected for 14 years from January 1, 1998, to December 31, 2011, at Point Petre (43.8430, −77.1540), Ontario, Canada, following IADN field sampling standard operation procedures.15 Briefly, an atmospheric sample was collected for 24 h every 24 days using a highvolume air sampler (General Metal Works, model GS2310). The sampler was equipped with a quartz fiber filter (Whatman QM-A) to first collect the particles and with a cartridge containing XAD-2 resin (40 g, 20−60 mesh) to trap the vaporphase chemicals. During the same time period, monthly precipitation samples, integrating all precipitation events each month, were collected using a MIC automated wet-only sampler (MIC Co., Thornhill, ON). Analysis. The vapor, particle, and precipitation samples were separately processed, following the Indiana University laboratory’s standard operating procedures.16 After the addition of surrogate recovery standards, samples were Soxhlet extracted for 24 h with 50% (v/v) n-hexane in acetone (OmniSolv Inc.). Extracts were fractionated through a water-deactivated silica column [3.5% for vapor and particle samples and 3.0% for precipitation samples (Fisher Scientific Inc.)]. The first fraction was eluted with 25 mL of n-hexane, and the second fraction was eluted with 25 mL of 50% (v/v) n-hexane in dichloromethane. The first fraction was concentrated and spiked with internal

measurement programs produced essentially equivalent concentration data. In this paper, the 1998−2011 data covering the vapor and particle phases and precipitation have been analyzed by the temporal trend calculation methods that we have developed and used since 2010.11,13 Using these approaches, we will present the concentrations of ∼110 polychlorinated and polycyclic compounds, their phase distributions, and their time trends and seasonal variations in air (both vapor and particle phases) and in precipitation. This is the first study that comprehensively investigates three classes of organic pollutants (PCBs, organochlorine pesticides, and PAHs) in atmospheric vapor and particle phases and in precipitation at Point Petre. In addition, we will compare the concentration and time trend data at Point Petre from the two study periods to determine how the rates and/or seasonal variations have changed with time.

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MATERIALS AND METHODS Sampling. The 1992−2003 concentration data from Point Petre for PCBs, pesticides, and PAHs in air and in precipitation have been reported piecemeal in various studies,4−8,10,14 and the sampling and measurement methods will not be repeated here. 227

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decreased from 1400 to 320 pg/L (t = −6.2; P < 0.001). These decreases are significant and substantial. The concentrations of endosulfan I in the vapor phase have also decreased from 110 to 50 pg/m3 (t = −2.6; P < 0.001) between the former and latter studies. On the other hand, the concentrations of endosulfan I in precipitation did not change significantly between the two studies. These results are consistent with endosulfan’s restriction in North America in 2010. The concentration changes for ΣPAH are a mixed bag. The vapor-phase concentrations increased significantly (t = 3.8; P < 0.001); the particle-phase concentrations decreased significantly (t = −3.0; P < 0.001), and the precipitation concentrations did not change significantly. Overall, it is likely that the concentrations of PAH between the two studies have not changed. The concentrations of ΣPCB in the vapor phase have not changed significantly between the two studies, suggesting there may be continuing sources of PCBs to the Point Petre atmosphere. Temporal Trends. We have analyzed the most recent Point Petre data (1998−2011) using an approach recently developed in our laboratory11,13 to assess long-term temporal trends. Concentration data in each phase were transformed to their natural logarithms and fit using a harmonic regression:11,13

standards for both PCBs (PCB-30 and PCB-204) and PAHs (d10-anthracene, d12-perylene, and d12-benz[a]anthracene), and the second fraction was concentrated and spiked with internal standards for both pesticides (PCB-65 and PCB-155) and PAHs. PAHs were analyzed on an Agilent 6890 series gas chromatograph (GC) coupled with a 5973 mass spectrometer (MS). A DB-5MS column (J&W Scientific, 30 m long, 250 μm inside diameter, and 0.25 μm film thickness) was used. PCBs and pesticides were analyzed on Hewlett-Packard 5890 and 6890 GC instruments equipped with 63Ni electron capture detectors and DB-5 and DB-1701 (J&W Scientific) 60 m columns (250 μm inside diameter and 0.1 μm film thickness). A total of 74 PCB congeners, 21 organochlorine pesticides, and 17 polycyclic aromatic hydrocarbons were analyzed. PCB data are available in the vapor phase (1999−2011) and in precipitation (2000−2011) but, because of low concentrations, not in the particle phase. Pesticide data are available in the vapor (1998−2011) and particle (1998−2003) phases and in precipitation (2000−2011). PAH data are available in the vapor and particle phases (1998−2011) and in precipitation (2000− 2011). Quality Control and Quality Assurance. The accuracy of the data was ensured by following quality control and quality assurance procedures. The detailed information is given in the IADN Quality Assurance Program Plan and the IADN Quality Control Project Plan.17,18

ln(C) = a0 + a1 sin(zt ) + a 2 cos(zt ) + a3t

(1)

where C is the pollutant’s concentration in picograms per cubic meter for the vapor or particle phase or in picograms per liter for precipitation, t is the time in Julian days starting from January 1, 1990, z is 2π/365.25 to fix the periodicity at 1 year, a0 is the intercept that rectifies the units, a1 and a2 are the harmonic coefficients that describe seasonal variations, and a3 is a first-order rate constant in inverse days. The time it takes for these concentrations to decrease by half (in years) is called a halving time, and it is given by

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RESULTS AND DISCUSSION Concentrations. The concentrations (arithmetic average ± standard error) of the individual and summed compounds in each phase, which were measured at Point Petre over the period from 1998 to 2011, are listed in Table S1 of the Supporting Information and shown as box plots in Figure S1 of the Supporting Information. The vapor-phase samples had higher concentrations of individual pesticides and total PAH (ΣPAH) than the particle-phase samples. This preferential association has been noted previously and is driven by the vapor pressures of the individual compounds, including phenanthrene as a part of the total PAH levels.6,19 Analysis of variance (ANOVA) results (listed in Table S1 of the Supporting Information) suggest that in each of the three phases the relative endosulfan concentrations are higher. This is consistent with the fact that the application of endosulfan was not restricted until 2010.20,21 Lindane or γ-HCH was banned in Canada in 2004 and in the United States in 2009, but it is still present at relatively high atmospheric concentrations; see Table 1. The equivalent data for the 1992−2003 study are summarized from the literature4−8,10 for comparison in Table 1. Because of the vast amount of data (two studies, >100 compounds, and three phases), we have elected to focus the comparison on four representative compounds or compound groups. These are γ-HCH, endosulfan I, ΣPAH, which is the sum of 17 individual PAH concentrations, and total PCB (ΣPCB), which is the sum of 74 individual PCB concentrations. Comparing the concentrations measured in the former study with those from the latter study shows that the concentrations of γ-HCH have decreased significantly between 1992 and 2003 and between 1998 and 2011 (Table 1). In this case, the average vapor-phase concentrations decreased from 12 pg/m3 in the 1992−2003 period to 6.6 pg/m3 in the 1998−2011 period (t = −4.7; P < 0.001), and the γ-HCH precipitation concentrations

t1/2 =

−ln(2) 365.25a3

(2)

Examples of these regressions for γ-HCH, endosulfan I, ΣPAH, and ΣPCB are shown in Figure 1. All of the regression parameters and halving times for all compounds and for all

Figure 1. Regressions using eq 1 of the vapor-phase concentrations at Point Petre, Ontario, from 1998 to 2011 (inclusive) as a function of sampling date of γ-HCH, endosulfan I, ΣPAH, and ΣPCB. All regressions are significant at P < 0.01, and all regression results are listed in Table S2 of the Supporting Information. The x-axis tick marks indicate the beginning of each year. For endosulfan I, the overall regression is highly significant, but the rate constant (a3) is not. 228

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phases are listed in Table S2 of the Supporting Information, and all significant halving times are shown in Figure S2 of the Supporting Information. The concentrations of all three classes of contaminants for all phases are significantly decreasing. During the 1998−2011 period, the concentrations of PCBs and PAHs generally decreased with halving times on the order of 10 years, while the halving times of pesticides were more variable (see Figure S2 of the Supporting Information). The calculated halving times for the four representative compounds are listed in Table 1. The halving times in the 1998−2011 study for the two pesticides are 2.0−4.0 years (with the exception of endosulfan I in precipitation at 7.4 years), and for ΣPAH and ΣPCB, the halving times are 9.3−12 years. As discussed above, PAH concentrations are not likely to be changing rapidly because of the continuity of their main source (combustion). The rate of change in PCB concentrations is more rapid than that calculated from the 1992−2003 observations (∼17 years)11 around the Great Lakes. This may indicate that PCBs are being eliminated from the atmosphere more rapidly than previously suspected, but even a halving time of ∼10 years is high given that the use and sale of PCBs have been restricted in the United States since 1976.22 This result, together with the similar average PCB concentrations between the former and latter studies (80 and 90 pg/ m3), suggests that there may still be significant continuing sources of PCBs to the Point Petre atmosphere, possibly including vaporization from PCB-contaminated soil or water,23,24 urban areas,25−29 or PCB-containing hazardous waste.30 With one exception, the halving times reported in the 1998− 2003 study are not significantly different from those calculated here from the more recent data. The one significant difference was the halving time of γ-HCH in the vapor phase. The halving time from the 1998−2003 study was 7.8 years, and from the more recent study, it was 4.0 years. The usage of γ-HCH in Canada was banned in 2004;6 thus, the faster reduction of γHCH concentrations measured at Point Petre in the latter study may be a result of this regulation effort. It is also worth noting that all of the halving times in Table 1 are positive, which means that these compounds are all disappearing from the atmosphere, even at slow rates. Seasonal Variations. Most of the regressions using eq 1 show statistically significant a1 or a2 coefficients, from which the seasonality of a given compound can be calculated (Table 1 and Figure S3 and Table S2 of the Supporting Information). Higher concentrations of individual pesticides and all PCB congeners in vapor-phase samples were consistently observed in midsummer (July or August). A major environmental source of PCBs now is volatilization from either primary sources or secondary sources,31 and this process is enhanced as the ambient temperature increases. In fact, we have previously modeled this behavior with the Clausius−Clapeyron equation.32 Elevated pesticide concentrations in the vapor phase in the summer could also be partially attributed to enhanced volatilization from contaminated soil or water during the warmer summer months. The concentrations of almost all PCBs and PAHs in precipitation and PAHs in the particle phase peaked in the winter (PCBs in March and PAHs in January). This could be a result of the scavenging efficiency of snow being higher than that of rain.4,5,33 Increasing emissions from space heating during the colder winter months is another reason for elevated PAH concentrations (in both the particle phase and precipitation) in the winter.34

Although variable, the maximal dates for pesticide concentrations in precipitation show two distinct patterns. The maximal concentrations of recently restricted pesticides, γHCH and endosulfans, were found in late spring to summer (May and June), suggesting that these pesticides may still being used on some crops around the Great Lakes.21,35 The concentrations of the pesticides that were banned early peaked in the winter (December to March), when enhanced partitioning to particles and effective scavenging by snow occur.5 Seasonal variations were rarely found for particle-phase pesticides and vapor-phase PAHs. Similar to the seasonality in precipitation, the maximal dates for the pesticides that were banned early (α- and γ-chlordane and dieldrin) in the particle phase were in the winter (late January and early February), while that of endosulfan I was in late spring (April 26). The maximal dates for PAHs, which have significant seasonal variations, are variable, ranging from August 20 to January 10. There are no significant differences between the measurements of these maximal dates in the 1998−2003 study and in the more recent one (Table 1), reflecting the consistency in the types of sources of these chemicals.

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ASSOCIATED CONTENT

S Supporting Information *

Tables and figures summarizing all abbreviations, concentration means and medians, ANOVA results, and output of the regressions using eq 1 for all compounds at all sites. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Indiana University Integrated Atmospheric Deposition Network Team for laboratory support. We acknowledge Environment Canada for funding the operation of the Point Petre station and supporting the sample collection and quality assurance/quality control data management. This work has been funded by the U.S. Environmental Protection Agency’s Great Lakes National Program Office (Grant GL995656, Todd Nettesheim, project officer).

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REFERENCES

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