Evaluation of Wipe Sampling Procedures and Elemental Surface Contamination

Abstract

Wipe sampling was performed on various surfaces in several environments to determine the characteristics of the wipe sampling procedure and measure ambient levels of selected elements. The samples were collected from 18 different locations in home, office, research laboratory, and outdoor environments. Wipe samples were collected by wetting smear tabs with two drops of distilled water, then wiping a 100-cm2 area in two orthogonal raster patterns. The samples were analyzed by proton-induced x-ray emission for determination of quantity of 72 different elements per sample. Reproducibility of the wipe sampling technique was determined by collecting two adjacent wipes and comparing the elemental compositions on both. The median ratio from 297 pairs of these samples was 1.0 with 50% of the detectable sample pairs having ratios between 0.6 and 1.5. This shows that the wipe sampling procedure does not have the degree of precision generally accepted in industrial hygiene practice. Efficiency of removing material from the surface was determined by collecting one wipe sample, then immediately wiping the same area with a second sample. The median elemental composition of the second sample was 55% of the first. (Interquartile range was 0.35 to 0.92.) Silicon, chlorine, potassium, calcium, titanium, nickel, copper, and zinc were found on all the samples. The highest median concentrations (in the microgram range) of all samples were magnesium, aluminum, silicon, chlorine, potassium, and calcium. Median concentrations in the tenths of a microgram range were noted for phosphorus, sulfur, titanium, iron, and zinc.