Surface sampling for a pesticide in dust and small spills of a solid dye

The aim was to determine whether a published sampling technique for loose soil on hard surfaces achieved acceptable efficiency at surface dust/soil coverages of 10-20 mg/ 100 cm2. The sampler was a cordless personal sampling pump operated at 4.0 L/min connected to a cassette containing a filter, the cassette being also connected to a Tygon sampling probe that was moved manually on the surface to be sampled. Rhodamine 6G dye dust was evaluated at 10 mg/100 cm2 coverage at flow rates of 1.0-4.0 L/min. Two National Institute of Standards and Technology (NIST) standard reference materials (SRMs) were used for pesticide experiments: SRM 2711 Montana Soil, and SRM 1649a Urban Dust. The efficiencies for these SRMs were determined uncoated, and coated with 1300 microg chlorpyrifos/g as a Lorsban 4E emulsifiable concentrate formulation. The 3-pass technique sampled both the pesticide-coated and uncoated dust and soil at >79 percent efficiency and at better than 16 percent coefficient of variation (CV) above 15 mg collected mass. Sampling at 20 mg/100 cm2 coverage lowered the CV to < or = 7.1 percent. The dye was sampled with similar efficiency > or = 1.5 L/min, but the CV for the 3-pass technique was <10 percent at 1.5-2.0 L/min, and <20 percent at 1.5-4.0 L/min. The efficiency for a 5-pass technique for the dye exceeded 90 percent at > 1.5 L/min with CVs < 10 percent at 1.5, 2.0, 2.5, and 3.5 L/min. The weight change of the sampling probe and the cassette must be measured for accurate determination of low surface coverages rather than just the weight change of the filter alone. The method allows use of personal sampling equipment for aerosols to measure low coverages of loose dust, soil, and chemical solids on hard surfaces.