S AMPLING AND E XTRACTION OF P ESTICIDES IN A MBIENT A IR Methods used for the sampling and extraction of pesticides in the atmosphere are not

10.2.1 S AMPLING AND E XTRACTION OF P ESTICIDES IN A MBIENT A IR Methods used for the sampling and extraction of pesticides in the atmosphere are not

diverse. Generally, the sampling is carried out by pumping the air onto traps and extraction of pesticides on traps are performed by solid –liquid extraction.

10.2.1.1 Sampling of Pesticides in Ambient Air Pesticides in ambient air are sampled by conventional high-volume samplers on

glass fiber or quartz filters followed by solid adsorbents, mainly polyurethane foam (PUF) or polymeric resin (XAD-2 or XAD-4), for the collection of particle and gas phases, respectively.

Depending on the high-volume sampler used, length or diameter of filters varied generally between 200 3 250 mm (Andersen sampler), 102 mm diameter (PS-1 Tisch

262 Analysis of Pesticides in Food and Environmental Samples

Rain protection Filter holder

XAD-2 resin holder

Flow meter

FIGURE 10.1 High-volume sampler developed in the LPCA. (From Scheyer, A., PhD thesis, University of Strasbourg, 2004.)

Environmental, Inc., Village of Cleves, OH) to 300 mm (LPCA collector, home made) diameter (Figure 10.1). Generally 10 –20 g of XAD-2 resin, a styrene–divinylbenzene sorbent that retains all but the most volatile organic compounds, is employed to trap the gaseous phase and is used alone or sandwiched between PUF plugs

(75 mm 3 37 mm). White et al. 33 used 100 g of XAD-2 resin between 2 PUF plugs. XAD has been previously used to collect a variety of pesticides including diazinon, chlorpyrifos, disulfoton, fonofos, mevinphos, phorate, terbufos, cyanazine, alachlor, metolachlor, simazine, atrazine, deethyl atrazine, deisopropyl atrazine, molinate, hexachlorobenzene, trifluralin, methyl parathion, dichlorvos, and isofenphos. 34

In a recent study, the efficiency of trapping gaseous current-used pesticides on different traps, including PUF, XAD-2 resin, XAD-4 resin, and PUF=XAD-2=PUF and PUF=XAD-4=PUF sandwich, was determined. 35 From this study, it appears that XAD-2 and PUF=XAD-2=PUF are the better adsorbent for current-used pesticides (27 pesticides tested) and the sandwich form is slightly more efficient than XAD-2 alone while PUF plugs is the less efficient.

Sampling and Analysis of Pesticides in the Atmosphere 263 The duration of sampling depends mainly on the purpose of the sampling and

on the detection limits of the analytical method used. Generally, sampling varied between 24 h and 1 week and the total air pumped varied between

A sampling time of about 24 h is generally sufficient to reach the detection limit of pesticides in middle latitude

250 m 3 , 36,37 525

3 , 33 and 2500 m 3 of air. 38

–1081 m

atmosphere and avoid clogging-up the filters. 39 –41

10.2.1.2 Extraction of Pesticides in Ambient Air After sampling, traps are separately extracted by using Soxhlet extraction with

different solvents used alone, such as acetone, 38 or as a mixture, such as 36% ethyl-

34 2 36,37 in n-hexane, (50:50) n-hexane=acetone, or (50:50) n-hexane=methylene chloride

acetate in n-hexane, 44 (85:15) n-hexane=CH

h. In some studies, the ASTM D4861 –91 method was followed. After Soxhlet extraction, extracts were dried with sodium sulfate and reduced to

0.5 mL using a Kuderna Danish concentrator followed by nitrogen gas evaporation 42 or were simply concentrated to about 1 mL by using a conventional rotary evapor-

ator. 36,37,41 Depending on the authors and on the analytical method used, a cleanup procedure

can be performed after concentration. Foreman et al. 42 passed extracts through a Pasteur pipet column containing 0.75 g of fully activated Florisil overlain with 1 cm

of powdered sodium sulfate. Pesticides were eluted using 4 mL of ethyl acetate into a test tube containing 0.1 mL of a perdeuterated polycyclic aromatic hydrocarbon used as internal standard. The extract was evaporated to 150 mL using nitrogen gas, transferred to autosampler vial inserts using a 100 mL toluene rinse. Sauret et al. 41 and Scheyer et al. 36,37 used GC –MS–MS for the analysis of airborne pesticides and they do not perform a cleanup procedure.

Badawy, 44 who used GC –ECD for the analysis of pesticides in particulate samples, concentrated Soxhlet extracts to 5 mL and firstly removed elemental sulphur by reaction with mercury. After that, extracts were quantitatively transferred to a column chromatography for separation into two fractions using 3 g of 5% deactived alumina. Fraction one (FI), which contains chlorobiphenyls, chloroben- zenes, and hexachlorocyclohexane, was eluted with 16 mL of n-hexane. Second fraction (FII), includes permethrin, cypermethrin, deltamethrin, and chloropyrophos (rosfin), was eluted with 6 mL of 20% ether in hexane.

In the 1990s, a method using fractionation by HPLC on a silica column was used for the cleanup of atmospheric extracts. 45,46 After extraction, samples were fraction-

ated on a silica column using an n-hexane=MTBE gradient for isolating nonpolar, medium-polar, and polar pesticides, which were analyzed by specific methods 46 including GC –ECD and HPLC–UV. In the method developed by Millet et al.,

three fractions were obtained; the first one contains pp 0 DDT, pp 0 DDD, pp 0 DDE, aldrin, dieldrin, HCB, fenpropathrin, and mecoprop, the second one contains methyl- parathion, and the third one contains aldicarb, atrazine, and isoproturon. This step was necessary since fractions 2 and 3 were analyzed by HPLC –UV, a nonspecific method.

264 Analysis of Pesticides in Food and Environmental Samples

10.2.1.3 Cleaning of Traps for the Sampling of Pesticides in Ambient Air Traps (XAD and PUF foam) were precleaned before use by Soxhlet successive

cleaning steps or by one cleaning step depending on authors. Scheyer et al. 36,37 precleaned the filters and the XAD-2 resin by 24 h Soxhlet (50:50) with n-hexane=

2 and stored them in clean bags before use, while Peck and Hornbuckle precleaned the XAD-2 resin with successive 24 h Soxhlet extractions with methanol, acetone, dichloromethane, hexane, and 50=50 hexane=acetone prior to sampling.

CH 2 Cl

Some authors (i.e., Coupe et al. 21 ) used a heater to clean filters (backing at 4508C for example). In all cases, a blank analysis is required to check the efficiency of the cleaning and storage before use.

The ultrasonic bath is poorly used for the extraction of filters and resins after 39 sampling. Haraguchi et al. used this technique for their study of pesticides in the atmosphere in Japan.