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Assessing Dicofol Concentrations in Air: Retrospective Analysis of GAPS Network Samples from Agricultural Sites in India Anita Eng, Ky Su, Tom Harner, Karla Pozo, Ravindra K Sinha, Babu Sengupta, and Mark Loewen Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.6b00041 • Publication Date (Web): 08 Mar 2016 Downloaded from http://pubs.acs.org on March 14, 2016

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Environmental Science & Technology Letters

Assessing Dicofol Concentrations in Air: Retrospective Analysis of GAPS Network Samples from Agricultural Sites in India Anita Enga, Ky Sua, Tom Harnera*, Karla Pozob,c, Ravindra K. Sinhad, B. Senguptae, Mark Loewenf a Air Quality Processes Research Section, Environment and Climate Change Canada, 4905 Dufferin St. Toronto, Ontario M3H 5T4, Canada b Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 753/5, 625 00 Brno, Czech Republic c Facultad de Ciencias Ambientales y Centro EULA-Chile, Universidad de Concepción, Casilla 160-C, Chile d Centre for Environmental Science, School of Earth Biological and Environmental Sciences, Central University of Bihar, Patna 800014, India e Central Pollution Control Board, Parivesh Bhavan, East Arjun Nagar, Delhi 110032, India f Freshwater Institute, Department of Fisheries and Oceans, Winnipeg, Manitoba R3T 2N6, Canada corresponding author: [email protected] ; tel. +1 416 739-4837

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Abstract

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Risk assessment of the pesticide dicofol is hampered by the lack of information on its levels which is largely attributed to its instability during instrumental analysis. In this study, dicofol was assessed in air through a novel approach by tracking the ratio of the two isomers (p,p’- and o,p’-) of its stable degradation product dichlorobenzophenone (DCBP), while considering other potential precursors. Twenty-three samples were collected using polyurethane foam (PUF) disk passive air samplers deployed across agricultural, urban, and rural sites throughout India in 2006 under the Global Atmospheric Passive Sampling (GAPS) Network. The retrospective analysis focused on agricultural sites in the Indo-Gangentic Plain region where dicofol is used. Yearly mean concentrations for p,p’- and o,p’-DCBP (breakdown products of p,p’- and o,p’-dicofol) in ng/m3 were (respectively) 1.1 and 0.29 for agricultural sites, 1.6 and 0.31 at an urban site, and 0.36 and 0.039 at a background site.

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1. Introduction

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Dicofol [2,2,2-Trichloro-1,1-bis(4-chlorophenyl)ethanol] is an organochlorine pesticide (OCP) that is used in the agricultural sector to control phytophagous mites on food, feeds, and crops (e.g. fruits, vines, ornamentals, vegetables, teas and cotton).1-3 Technical dicofol is also the hydroxylated derivative of dichloro-diphenyl-trichloroethane (DDT). During dicofol synthesis, p,p’- and o,p’-DDT are formed as intermediate compounds.4 While p,p’-DDT is efficiently converted to p,p’-dicofol, o,p’-DDT is not readily chlorinated, and is left behind as an impurity;4,5 thus the existing use of dicofol may also be an important source of o,p’-DDT to the environment.

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Technical dicofol, which is produced primarily as two isomers (80% p,p’-dicofol and 20% o,p’dicofol) is structurally similar to DDT (Figure S1) and poses similar concerns with respect to its release and presence in the environment. These include its potential for long range transport, persistence in the environment, bioaccumulation, and deleterious health effects to humans and wildlife.6-11 These persistent organic pollutant (POP)-like characteristics of dicofol have led to international scrutiny via the Stockholm Convention on POPs, and resulted in the development of a draft risk profile by the Persistent Organic Pollutants Review Committee (POPRC) – the first step in the process for listing a new POP under the Convention. Currently, there is limited data on the levels of dicofol in air.12

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Efforts to measure dicofol in air and to assess its long-range transport potential have been hampered by the relative instability of dicofol that results in its decomposition during instrumental analysis of environmental samples and standard solutions.13 Dicofol is also degraded in the natural environment.1,3,14,15 The main breakdown product for dicofol is the compound dichlorobenzophenone (DCBP) that has similar POP-like characteristics as dicofol but is substantially less prone to degradation during instrumental analysis.13 Consequently, dicofol can be viewed as a precursor chemical to its stable degradation product DCBP. In this study, we assess dicofol in air by monitoring its stable degradation products p,p’- and o,p’-DCBP (Figure 1). We also check for consistency between DCBP isomer ratios and dicofol isomer ratios as validation that the levels of DCBP reflect fresh use of dicofol versus DCBP that originates from other precursor chemicals and/or secondary sources (environmental processing). This approach is outlined in the results and discussion, with 3 criteria that need to be met for assessing dicofol levels in air based on DCBP. This approach was applied retrospectively to air samples collected in 2006 across India under a Global Atmospheric Passive Sampling (GAPS) network special study.16 India was identified by Li et al. (2015)1 as a major consumer of dicofol, with usage ranging from 145 t in 2000 to 45 t in 2012 and mainly in the Indo-Gangetic Plain region in northern India. This study represents the first comprehensive spatial assessment of dicofol levels in air based on its degradation product DCBP using passive air samplers, with an emphasis on sampling sites located in India’s Indo-Gangetic Plain region. Considerations have been made for the other potential precursors to DCBP such as the pesticides chlorobenzilate, chloropropylate and DDT.17

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2. Materials and Methods

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2.1. Passive Air Sampler Preparation and Deployment. Sampler preparation and analysis were carried out at the Hazardous Air Pollutants (HAPs) Laboratory at Environment and Climate Change Canada in Toronto. The passive air sampler housings (TE-200, Tisch Environmental, Ohio) were cleaned with soapy water and solvents (acetone, petroleum ether, and dichloromethane) prior to deployment. The polyurethane foam (PUF) disks (Tisch Environmental, Ohio) were pre-cleaned using Soxhlet extraction in acetone (24 hours) followed by petroleum ether (24 hours). The PUF disks were stored in Teflon sealed, solvent rinsed 1 L amber glass jars at all times prior to and after sampling. Each PUF disk was deployed for approximately 3 month durations over four consecutive sampling periods during 2006. Field blanks (n = 3) were collected by placing a clean PUF disk into the housing for ~ 1 minute, then removing it and

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treating it as a sample. A more detailed description of sampler preparation and deployment is described in Pozo et al. (2011).16

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2.2. Study Area. PUF disk passive air samplers were deployed across several Indian agricultural regions in 2006-2007. This was conducted as a sub-project of the GAPS Network.16 In this study, 6 sites were chosen from the 2006 archived sample extracts (which were stored in GC vials in the freezer) with a focus on sites located in the Indo-Gangetic Plain region, where dicofol is most heavily used.1 This includes 4 agricultural sites (Laksar in Uttaranchal, Delhi C and Delhi D in Haryana, and Mudhol in Karnataka), 1 urban site (Patna in Bihar), and 1 background site (Surkanda Devi in Uttaranchal). The agricultural site Mudhol is located outside of the Indo-Gangetic Plain region. The background site Surkanda is located at a high altitude, and within a completely forested area in the Himalaya near Mussoorie. The passive air samplers were deployed in representative areas (e.g. agricultural regions) but were situated far enough from sources so as not to be dominated by application events (e.g. spraying). The samplers were mounted more than 5 m above ground level in areas with unobstructed airflow. Detailed site descriptions and coordinates are reported in the supporting information of Pozo et al. (2011).16

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2.3. Sample Extraction and Analysis. A total of 23 samples and 3 field blanks were extracted and analyzed. Details of sample extraction and cleanup are presented elsewhere.18,19 Sample extracts were analyzed using an Agilent 7890B/7000C gas chromatography/mass spectrometry (GC/MS) Triple Quadrupole (QQQ) system, and details of analytical methods are presented in Text S1 in the supporting information (SI). In short, p,p’-dicofol, o,p’-dicofol, p,p’-DCBP and o,p’-DCBP were analyzed using electron capture negative ionization (ECNI) in selected ion monitoring (SIM) mode since negative chemical ionization (NCI) exhibited high sensitivity for these compounds compared to multiple reaction monitoring (MRM) electron impact (EI) mode. The precursor and product ions are listed in Table S1. D8 p,p’-dicofol was used as the internal matching standard, and was added to all sample extracts and calibration standards to monitor its break down to D8 p,p’-DCBP during instrumental analysis. Complete breakdown of D8 p,p’-dicofol to D8 p,p’-DCBP was observed in the sample matrix and near-complete (~90%) break down was observed in the standards (n = 5) as shown in Figure 1 and Figure S2.

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It is noteworthy that attempts were made to minimize dicofol degradation on the GC/MS by using pulsed injection (versus splitless injection) as described by Zhong et al. (2012).20 Although the pulsed injection did in fact reduce the extent of dicofol degradation, the behaviour was highly variable and not consistent between native and labelled D8 dicofol. Therefore, we decided to minimize this uncertainty by analyzing all samples in splitless injection mode, and thereby forcing the nearly complete conversion of dicofol to DCBP.

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Additionally, p,p’-DDT and o,p’-DDT were analyzed in sample extracts to compare with levels reported by Pozo et al. (2011)16. This was done to check that the DDT isomers have not degraded during sample storage (with possible conversion to DCBP) and also to confirm the relative isomer proportions of DDT and dicofol in air samples, since technical dicofol comprises 1-2% p,p’-DDT and 2-18% o,p’-DDT as an impurity.5 In the current study, p,p’- and o,p’-DDT were analyzed with improved detectability and

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sensitivity using MRM EI mode with splitless inlet injection, and using mirex as the internal standard. The precursor and product ions are listed in Table S2.

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2.4. Deriving Air Concentrations Based on Estimated Air Volumes. The conversion of the amount accumulated in the passive air sampler to a concentration in air involves the derivation of an effective air sample volume, as is done under the GAPS Network.21,22 Linear uptake can be assumed for the dicofol isomers for the entire sampling period because of their low volatility and high octanol-air partition coefficient (KOA),1,23,24 which translates to a high sorption capacity for the PUF disk. Therefore, the equivalent air volume is simply the product of the linear gas-phase sampling rate of the PUF disk sampler and the deployment time. For this estimation of the air volume, we used site-specific sampling rates reported in Pozo et al. (2011)16 that were based on depuration compounds added to samples prior to deployment. The sample deployment times are also reported in Pozo et al. (2011)16 and ranged from 45 to 95 days. The resulting air volumes were on average in the range of approximately 200 to 300 m3.

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3. Results and Discussion

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3.1. Criteria Needed to Assess Dicofol Concentrations in Air Based on DCBP. Figure 1 shows a chromatogram of a p,p’- and o,p’-dicofol standard, in which dicofol is intentionally converted to its stable degradation products p,p’- and o,p’-DCBP respectively. By monitoring these DCBP isomers in the air samples and ensuring complete conversion from dicofol to DCBP, the variability in sample analysis (e.g. due to the extent of dicofol degradation in each sample) is minimized. Analysis of PUF disk field blanks (n = 3) for p,p’-DCBP and o,p’-DCBP revealed that concentrations were negligible relative to the samples. The lowest levels detected in samples were at least 8 times greater than in the field blanks. The method detection limits (MDLs) in pg/m3 were calculated as the field blank mean (FBM) plus three standard deviations (SD), based on an average estimated air sample volume of 300 m3. The MDLs for p,p’-DCBP and o,p’-DCBP were 4.4 and 1.8 pg/m3 respectively.

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The ability to force the complete conversion of dicofol to its stable degradation product DCBP during instrumental analysis in a repeatable manner provides an opportunity to indirectly assess dicofol concentrations in air based on levels of DCBP. In order for this approach to be successful, the following conditions must be satisfied.

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(i)

(ii)

(iii)

Instrumental analysis must result in complete or near-complete and consistent conversion of p,p’- and o,p’-dicofol isomers to its p,p’- and o,p’-DCBP isomers, respectively (i.e. the isomer ratios for the two components of dicofol (approximately 80% p,p’- and 20% o,p’-)5 are conserved when they degrade to the two isomers of DCBP). Instrumental analysis must not result in conversion of precursor compounds present in the samples to DCBP, with the exception of dicofol (e.g. other possible precursors include DDT, chlorobenzilate, chloropropylate). Secondary sources of DCBP must be assessed and shown to contribute negligibly to the levels of DCBP in air. Possible secondary sources include:

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a. DCBP formed from DDT degrading in the natural environment (from technical DDT or the DDT as an impurity in dicofol). b. DCBP formed from dicofol degrading in the natural environment.

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The first criterion (i) is easily met using standard solutions and labelled surrogates, as described previously in our materials and methods section and presented in Figure 1. Our results in Figure 2a and Table S3 show the isomeric percent composition of DCBP is remarkably similar across all agricultural and urban sampling sites, with p,p’- and o,p’-DCBP comprising on average 80% and 20% (± 7% SD) respectively of the total.

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The second criterion (ii) is also met in this study. Using standard solutions we have confirmed that DDT does not convert to DCBP during instrumental analysis. We have also shown that DDT does not degrade during sample extract storage over long periods, since re-analyzed levels of DDT in the current study were comparable to or higher than those reported in Pozo et al. (2011).16 Thus, the DDT present in the samples can be eliminated as a potential source of DCBP that could interfere with our sample analysis. Other known precursors of DCBP include the pesticides chlorobenzilate and chloropropylate.17 However, according to the World Health Organization (WHO), chlorobenzilate and chloropropylate are classified as ingredients that are obsolete or discontinued for use as pesticides,25,26 and therefore should not be present in the air samples at levels that would interfere with our analysis.

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3.2. DCBP as Secondary Emissions from DDT or Dicofol. The remaining criterion (iii) is the possibility that the presence of DCBP in our air samples could be due to secondary emissions of DCBP (e.g. from soil, water) that has originated from DDT or dicofol. Numerous studies have proposed different DDT degradation pathways to form DCBP.27-29 However, DDT does not degrade to DCBP directly. This transformation pathway involves the intermediate compounds 1,1-dichloro-2,2,-bis(pchlorophenyl)ethylene (DDE) and/or 1,1-dichloro-2,2,-bis(p-chlorophenyl)ethane (DDD), which are both known to be stable in the environment.30 Though technical DDT also comprises 80% p,p’- and 20% o,p’DDT isomers,31 Huang et al. (2001)32 and Meijer et al. (2001)33 reported that the transformation rates of the p,p’-isomers of DDT and DDD were faster than those of the respective o,p’-isomers in sediment slurries and soil respectively. This physiochemical difference would result in substantial enrichment of p,p’-DCBP (i.e. > 80%) in air relative to the o,p’-isomer. The fact that this enrichment in p,p’-DCBP was not observed in our study (Figure 2a, Table S3) is a strong indication that these DDT-derived secondary sources of DCBP are not contributing substantially to what we measure in the air samples. The possible exception is at the background site Surkanda where there was some enrichment of p,p’-DCBP (91% ± 5%) that could be attributed to contributions from secondary emissions tied to the DDT use in India by the fate pathway described above.

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Studies have also investigated the degradation of dicofol to DCBP under different conditions in the environment.14,17,34 In both soil and water, o,p’-dicofol degrades more rapidly than p,p’-dicofol to its respective DCBP isomer.17 Since technical dicofol comprises 80% p,p’- and 20% o,p’-,5 the differing degradation rates between these two dicofol isomers would shift this isomer proportion when converted to its respective DCBP isomers (i.e. o,p’-DCBP > 20%). Our study results (Figure 2a, Table S3) shows a very consistent p,p’- and o,p’-DCBP percent composition of approximately 80% and 20% (± 7% 5



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SD) respectively, thus DCBP from dicofol degrading in the environment also does not contribute substantially to our samples.

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3.3. Seasonal Trends and Air Concentrations of Dicofol (Based on DCBP) and DDT. With criteria (i), (ii) and (iii) satisfied, we can conclude the p,p’- and o,p’-DCBP concentrations detected in our samples reflect levels in air for p,p’- and o,p’-dicofol, respectively, that have resulted from our induced transformation of dicofol during GC/MS instrumental analysis. Figure 2a and Table S3 shows that the 80% p,p’- and 20% o,p’- isomeric ratio is conserved in the levels of DCBP detected in samples, which indicates fresh inputs of technical dicofol to air in the study area. Yearly mean concentrations of DCBP (sum of p,p’- and o,p’- isomers) in air across Indian sites are summarized in Figure 2b, and by quarterly sampling periods in Table S3. Levels were in the range of about 1-2 ng/m3 across the agricultural sites in the Indo-Gangetic Plain region, and 2 ng/m3 at the urban site Patna. At the background site Surkanda, levels in air were lower and averaged 0.4 ng/m3. Of the four agricultural sites, the lowest concentration was observed at Mudhol which lies well south of the Indo-Gangetic Plain region, which is the main dicofol-use region.1 In the original study by Pozo et al. (2011),16 OCP concentrations in air were also relatively low at this site.

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A secondary objective of the study was to re-analyze samples for DDT using improved methodology and to compare this with the results reported by Pozo et al. (2011).16 We also checked the ratio of o,p’-DDT/p,p’-DDT in the samples, as previous studies have shown that DDT in the environment originating from technical dicofol production results in enrichment of o,p’-DDT.5,35-39 Consequently, the o,p’-DDT/p,p’-DDT ratio for technical dicofol is much higher than the 0.2-0.3 ratio reported for technical DDT.39-42 For instance, the average o,p’-DDT/p,p’-DDT ratio of 7.0 has been reported for technical dicofol.5,35 In this study, the o,p’-DDT/p,p’-DDT ratios across all agricultural and urban sites had an average of 0.3 ± 0.08 (Table S3), indicating that DDT detected in the samples are mainly associated with ongoing use of technical DDT and not to the use of dicofol. The findings of this analysis are summarized in the SI (Text S2).

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Seasonal differences in air burdens of p,p’-DCBP and p,p’-DDT are shown in Figure S3, with highest levels in the period of April to September. India’s climate consists of 4 seasons, which roughly overlaps with the sampling periods used in this study. The winter period is from December through February where weather conditions are cool and dry; then a dry and hot summer from March through May; a southwest monsoon from June through September, and a second northeast monsoon period from October through November. Concentrations of p,p’-DCBP and p,p’-DDT were elevated in air samples collected during the warmer summer months and during the two monsoon periods. This is likely attributed to an increased application of insecticides, as the warm and wet climate provides favourable breeding conditions and higher hatching rates for insects.35,43 The seasonal trends observed in this study are also consistent with the OCP concentrations reported in Pozo et al. (2011)16 for hexachlorocyclohexanes (HCH), endosulfans, and chlordanes.

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To conclude, we have proposed, demonstrated and validated an approach for assessing dicofol concentrations in air by tracking its stable breakdown product DCBP. We recommend that the consistency in the ratio of the DCBP isomers (when compared to the isomers of technical dicofol) be 6


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used as a check to ensure that DCBP is derived from fresh dicofol application versus secondary sources and/or formation from other precursor chemicals. It is hoped that this method will help to address information needs on dicofol and that findings will contribute to the assessment of dicofol as a candidate POP, and specifically to its occurrence and distribution in air.

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Acknowledgements

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We thank Sum Chi Lee for her assistance with GAPS Network coordination, Liisa Jantunen for her input in dicofol method development and comments and Hayley Hung for her review of the manuscript and useful suggestions. We would also like to acknowledge the Chemicals Management Plan (CMP) and the United Nations Environment Programme (UNEP) for their support.

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The authors declare no competing financial interest

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Supporting Information Available: Additional details on methodology, re-analysis of DDT, four additional figures, and three tables summarizing results. This material is available free of charge via the Internet at http://pubs.acs.org

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p,p’-DCBP (13.053 min)

o,p’-DCBP (12.750 min)

p,p’-dicofol (15.081 min)

o,p’-dicofol (15.020 min)

359 360 361

Figure 1. ECNI TIC (total ion current) chromatogram of a p,p’- and o,p’-dicofol standard analyzed in splitless injection mode, which is intentionally converted to its stable breakdown products p,p’- and o,p’-DCBP respectively.

Percent Composition

Concentration in Air

91% 78%

78%

80%

82%

1.9 ng/m3 1.1 ng/m3 0.40 3 ng/m

Surkanda Delhi C

1.2 ng/m3

1.9 ng/m3

Surkanda Delhi C

Laksar

Delhi D

Laksar

Delhi D Patna

INDIA

Patna

85%

INDIA 0.18 ng/m3

Mudhol

Mudhol Σ DCBP (p,p’ + o,p’) Agricultural p,p’-DCBP

a. 362 363 364

o,p’-DCBP

Urban

b.

Background

Figure 2. Results from 2006 GAPS network special study across 6 sites in India showing a.) the percent composition of the two DCBP isomers and b.) yearly mean concentrations in air of dicofol’s breakdown product DCBP (sum of

11



365 366

p,p’- and o,p’- isomers). Error bars represent the standard deviation of the 4 quarterly samples at each site. Note: results for Mudhol represent the first 3 sampling periods in 2006.

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Assessing Dicofol Concentrations in Air: Retrospective Analysis of GAPS Network Samples from Agricultural Sites in India Anita Enga, Ky Sua, Tom Harnera*, Karla Pozob,c, Ravindra K. Sinhad, B. Senguptae, Mark Loewenf a Air Quality Processes Research Section, Environment and Climate Change Canada, 4905 Dufferin St. Toronto, Ontario M3H 5T4, Canada b Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 753/5, 625 00 Brno, Czech Republic c Facultad de Ciencias Ambientales y Centro EULA-Chile, Universidad de Concepción, Casilla 160-C, Chile d Centre for Environmental Science, School of Earth Biological and Environmental Sciences, Central University of Bihar, Patna 800014, India e Central Pollution Control Board, Parivesh Bhavan, East Arjun Nagar, Delhi 110032, India f Freshwater Institute, Department of Fisheries and Oceans, Winnipeg, Manitoba R3T 2N6, Canada corresponding author: [email protected] ; tel. +1 416 739-4837

Attribution for background photo in TOC Art: Imagery ©2016 DigitalGlobe, Map data ©2016 Google Link:https://www.google.ca/maps/place/28%C2%B040'00.0%22N+77%C2%B014'00.0%22E/@28.6544276,77.2391 119,3195a,20y,41.03t/data=!3m1!1e3!4m2!3m1!1s0x0:0x0


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