Ann. occuj?. Hyg.. Vol. 40, No. 5, pp. 525-530. 1996 Copyri&t Q 1996 British Occupational Hygiene Society

Published by Elsevier Science Ltd. Printed in Great Britain 0003-4878/96 $IS.OO+O.oO

Pm !%003-4878(96)0

THE EFFECT OF STORAGE, HANDLING AND TRANSPORT TRAUMAS ON FILTER-MOUNTED DUSTS

Saeed Awan and Gary Burgess Centre for Occupational Health, University of Manchester, Manchester Ml3 9FT, U.K.

(Received in jinal form 1 November 1995)

Abstract-The loss of material from dust-loaded filters was examined using five load ranges of four types of dust. Twelve replicate samples for each load range and dust type, a total of 240 samples, were collected on glass-fibre filters in the laboratory. Three of each group of 12 loaded filters were subjected to one of four levels of trauma: gentle shaking; dropping from table height; posting; or no trauma (control). The percentage weight loss was calculated for each sample.

Weight loss from the control and shaken filters was low with a mean loss of 10.4% (SD = 15.4) and 5.2% (SD = 11.8), respectively. Weight loss from the dropped and posted filters was much higher (mean losses of 68.2 and 54.4% with SDS of 18.8 and 27.9). The pattern of weight loss with increasing load varied with type of dust, being most marked for wood dust. The amount of loss following dropping or posting was also related to initial load. Three-way analysis of variance suggested strong interactions among dust type, load and trauma, with main effects for initial load and trauma being significantly related to percentage weight loss. Copyright 0 1996 British Occupational Hygiene Society.

INTRODUCTION

Concerns have been expressed about the loss of dust or filter material from dust- loaded titers during their post-sampling handling prior to gravimetric or chemical analysis. In some cases, post-sampling procedures entail only a short walk from the workplace to a laboratory where the filters are removed and placed on a balance. More usually, considerable handling may be involved, including transfer of the dust- loaded filters to plastic filter-pots which are transported or posted to laboratories. During these procedures the filters may undergo trauma leading to the potential for dust loss and for an underestimate of the exposure.

Puskar et al. (1991) investigated post-sampling dust loss from PVC filters loaded with three kinds of pharmaceutical dust. They reported that only 22% of the active ingredient could be extracted from the filters; 62% was found to be clinging to the internal walls and 16% to the inside of the bottom of the sampling cassette. They attributed these losses, in part, to electrostatic build-up. Demange et al. (1990) documented losses of up to 100% of dust during transit owing to particle deposition on filter holder inner walls.

By contrast, a recent study by Van Tongeren et al. (1994) reported an average loss of 0.04 mg after transit from filters loaded with 0.04-17.6 mg of respirable carbon black dust. The loss was not statistically significant, although 30 of the 120 filters tested displayed visible dislodgement of dust or filter damage after transit and were not included in the final analysis. The rejection of 25% of filters will have contributed to the lower losses reported.

525

526 S. Awan and G. Burgess

The Health and Safety Executive (HSE, 1993) prescribes procedures for the collection and analysis of dusts collected on glass-fibre (and other) filters, specifying that handling may result in a significant loss of glass-fibre filter material unless a minimum of 1 mg of dust is collected. Otherwise, no procedural guidance is offered to avoid post-sampling transport and handling traumas. Guidance on the maximum loading of filters-no greater than 2 mg of dust-is given in the United States (NIOSH Method No. 005, NIOSH, 1987), but no such limit has been specified in the U.K. The U.S. guidance is specific to PVC filters, however, and in practice, may prove difficult to observe as prior estimation of dust levels in the air is required, and concentrations may change during the sampling survey.

The present study was designed to investigate the effects of dust type, load and handling trauma on the loss of dust from filters, and specifically to answer two questions.

(1) What proportional loss (or gain) in weight occurs when filters (placed in plastic transport containers) are dropped, shaken or transported and posted?

(2) Do patterns of proportional weight loss (or gain) vary with different dusts or weight loadings?

MATERIALS AND METHODS

Sampling Four types of dusts were used for the study: talcum powder, wheat flour, wood

dust, and photocopying toner. These dusts were chosen for availability and relevance to occupational exposures. The materials were placed inside a 20-l. glass container and agitated using either a magnetic stirrer (for talcum powder and photocopying toner) or compressed air (for wheat flour and wood dust). Pre-weighed glass-fibre filters (25 mm Whatman GF/A), housed in seven-hole conductive plastic sampling heads, were inserted into the container from the top. Constant flow pumps (SKC Model 224-PCXR3) were used for sampling the air within the container. The first four filters for each dust were used to determine the rate of dust generation, with sampling time being varied to collect dust within a targeted load range. Five load ranges for each dust were obtained (< 1, 1.00-4.99, 5.00-9.99, 10.00-14.99 and 15.00-19.99 mg). Twelve samples for each dust load range were obtained by repeating three times the sampling for each load range. The filter weight was determined immediately after sampling.

Post-sampling treatment After weighing, the dust-loaded filters were immediately transferred to clean

plastic ‘filter-pots’ (Analyslide Cat. No. 7231, Gelman Sciences). The 12 filters in each dust-load category were divided into four groups of three filters. The first group was placed on a flask shaker (dust side up) and shaken for 1 h. The filter-pots in the second group were dropped from table height to a hard tiled laboratory floor (91 cm high). The filter cassettes in the third group were stacked upright, packed in polythene bubble wrap and packaged in a small cardboard box. The box was transported by car from the laboratory to a destination 2 h away and posted back to the laboratory unopened. The fourth group was weighed and kept in the laboratory

Effects of traumas on filter dusts 521

as a control. All the filters were reweighed immediately after the trauma. Initial and final weights were recorded and the percentage change in weight calculated.

Statistical methods Loss of material from dust-loaded filters can be expressed as either absolute mass

or as a proportion of the loading. In the present study it was assumed that the absolute loss would reflect the initial loading, and the question of interest was whether higher loadings lost proportionately more than lower ones. Thus the analysis reported here considered the percentage of the initial load that was lost when subjected to different types of trauma.

The distribution of percentage loss deviated significantly from normal, and exploratory transformations of the data did not reduce the skewness sufficiently for parametric techniques to be used with confidence. Initial analysis was carried out using a Kruskal-Wallis non-parametric analysis of variance (Siegel, 1956) to test the effect of dust type, initial load and trauma on weight loss. In this procedure all samples were ranked by the weight loss recorded and the probability of an unequal distribution across categories was tested by the x2 statistic. This technique does not provide a formal test of the effects of more than one factor, or of interactions, however, and to investigate these, parametric analysis of variance was used.

RESULTS

The median weight loss from the 240 samples was 28.4%, with a mean of 34.5% (SD= 33.4). Weight gain was recorded only in three samples. One toner powder control sample with dust-load range 1 (< 1 mg) gained 2.02% weight from sampling to final weighing. A photocopying toner control sample with dust-load range 1 also gained (1.85%) in weight at final weighing. The only sample to gain weight after it was subjected to an experimental trauma was a photocopying toner sample with weight in the range 10.00-14.99 mg, which was subjected to the shaking trauma and gained 9.52% in weight. These gains may have been caused by moisture absorption, errors in weighing or contamination from the filter pots.

Efect of dust type on percentage weight loss The mean, median and standard deviations for percentage weight loss according

to dust type are given in Table 1, together with Kruskal-Wallis ranking order of the dusts. The x2 value associated with the ranking (x2= 2.95, P=O.4) suggests that the type of dust used in this experiment was not significantly related to weight loss.

Table 1. Percentage weight loss by dust type

Type of dust

Talc powder Wheat flour Wood dust Photocopy toner

Median loss Mean loss Mean Kruskal-Wallis N W) (“/I rank order

60 31.0 37.3 37.1 128.8 60 40.0 34.5 30.8 118.7 60 21.4 35.4 35.3 125.7 60 23.8 31.0 30.5 108.8

528 S. Awan and G. Burgess

Table 2. Percentage weight loss by dust load range

Load range (w)

(1.00 1.00-4.99 s.ock9.99

10.00-14.99 15.00-19.99

N

48 48 48 48 48

Median loss Mean loss (%I (%I

8.7 28.0 23.8 30.0 36.7 39.0 50.1 39.0 35.6 36.8

0

35.0 29.0 34.8 34.8 32.1

Mean Kruskal-Wallis rank order

_-.- - 98.8

113.8 128.9 132.2 128.8

Table 3. Percentage weight loss pattern by trauma

Trauma Median loss Mean loss Mean Kruskal-Wallis

N vi) (%I rank order

Control (lab storage, 60 3.2 10.4 15.4 71.4 repeat weighing)

Gentle shaking 60 0.6 5.2 11.8 53.9 Dropping 60 71.1 68.2 18.8 189.3 Transport/posting 60 61.4 54.3 27.9 161.4

Efect of dust load on percentage weight loss There appears to be a trend towards increased percentage weight loss as the dust

load increases (Table 2), with the trend most evident for load range l-4 (< 1-14.99 mg). The Kruskal-Wallis ranking order of the load ranges is also consistent with increased likelihood of percentage weight loss with increasing load range, with an overall x2 = 7.9, P = 0.09.

Eflect of traumas The type of trauma was an important factor for percentage weight loss (Table 3),

with dropping and posting causing the greatest loss. The Kruskal-Wallis ranking order produces a x2 = 158.0 (P<O.OOl) indicating a significant association between percentage weight loss and trauma, with dropping producing the greatest weight loss and shaking the least.

Combined effects of dust type, load and trauma Percentage weight loss appeared to increase with initial load (range 1-5) for

wood dust and toner but only that for wood dust reached significance in the Kruskal-Wallis test [Table 4(a)]. Similarly, while there was a trend towards increased loss with increased initial load for all types of trauma, this reached significance only for dropping and for posting [Table 4(b)].

The results of the exploratory parametric analysis of variance to investigate the effects of all three factors (type, load and trauma) and their interactions on percentage weight loss are shown in Table 5. It will be seen that, as might be expected from Table 4, there are strong two-way and three-way interactions between the three factors. Even after accounting for interactions, trauma and initial load appear strongly related to proportional loss but the effect of dust type is less evident.

Effects of traumas on filter dusts 529

Table 4. Relation of dust load to percentage weight loss: summary of Kruskal-Wallis test for (a) dust type and (b)

trauma

N X2

(a) Dust type Talc powder Wheat flour Wood dust Photocopy toner

(b) Traumas Controls Shaking Dropping Transport/posting

60 0.780 0.941 60 4.067 0.937 60 13.426 0.009 60 7.280 0.122

60 5.276 0.260 60 3.736 0.443 60 11.576 0.021 60 27.979 <O.OOl

P

Table 5. Analysis of variance of percentage weight loss by dust type, load and trauma

Source of variation sum of squares

Degrees of freedom

Mean square F P

Main effects Dust type 1269.38 3 423.13 1.94 0.125 Load range 5117.60 4 1279.40 5.87 <O.OOl Trauma 178 186.23 3 59 395.41 272.26 <O.OOl

Two-way interactions Load-dust 14698.58 12 1224.88 5.62 <O.OOl Trauma-dust 7324.51 9 813.83 3.73 <O.OOl Load-Trauma 12 131.85 12 1010.99 4.63 <O.OOl

Three-way interactions Dust-load-trauma 13 530.17 36 375.84 1.72 0.012

Explained 232 258.30 79 2939.98 13.48 <O.OOl Residual 34905.17 160 218.16 Total 267 163.47 239 1117.84

DISCUSSION

The aim of personal sampling carried out in the workplace is to estimate exposure as accurately as possible. Any potential source of bias may lead to erroneous conclusions about the need for control measures, and lead to misclassification of exposure in risk assessments or epidemiological studies.

The results of the present study support the earlier results of Puskar et al. (1991), who reported losses of up to 88% of the active ingredient of pharmaceutical dusts from sampling cassettes during transit from the sampling site to the laboratory, and contrast with those of Van Tongeren et al. (1994), who found no significant loss of respirable carbon black dust after transit, after excluding filters with visible dislodgement of dust.

Since it is evident that, at least in some situations, significant loss can occur, it is suggested that the following steps could be taken to minimize the underestimation of occupational exposure to airborne dusts.

530 S. Awan and G. Burgess

(a) Light-weight, sealable and electrostatic-free filter holding cassettes should be used for the storage and transportation of the dust loaded filters. Filters should remain in the cassettes from pre-sample weighing to the final weight determination. Some particulate sampling cassettes have been designed for this purpose (Institute of Occupational Medicine Inhalable Dust Sampler).

(b) Whenever analysis is required which necessitates removal of the filter from the cassette, procedures should be introduced to ensure that materials potentially lost from the filter during handling or transit are completely extracted from the inside of the filter container.

(c) More work needs to be done to ascertain and quantify the impact of potential traumas on different dusts. Further studies are needed to explore the factors which may aggravate or reduce the handling and transit losses of the collected dusts from filters. Investigations should determine filter adhesion of various particulate materials from samples actually collected in the workplace, observing variations with dust particle size, electrostatic characteristics, moisture, humidity and temperature.

Acknowledgements-The study reported in this paper was carried out by Saeed Awan while on secondment from the Centre for the Improvement of Working Conditions and Environment, Directorate of Labour, Welfare Government of the Punjab, Pakistan, financed with a Foreign and Commonwealth Scholarship and Awards Scheme (FOCAS) in partial fulfilment of the requirements for the degree of Master of Science of the University of Manchester.

REFERENCES

Demange, M., Gendre, J. C., Herve-Bazin, B., Carton, B. and Peltier, A. (1990) Aerosol sampling difficulties due to particle deposition on filter holder inner walls. Ann. occup. Hyg. 34, 399403.

HSE (1993) General methods for the gravimetric determination of respirable and total inhalable dust. MDHS 14. Health and Safety Executive. HMSO, London.

NIOSH (1987) Analytical method No. 0500: Total nuisance dust. National Institute for Occupational Safety and Health Mznual of Analytical Methodr @HEW/NIOSH Publication No. 84-100). National Institute for Occupational Safety and Health, Cincinnati, Ohio.

Puskar, M. A., Harkins, J. M., Moomey, J. D. and Hecker, L. H. (1991) Internal wall losses of pharmaceutical dusts during closed-face, 37-mm polystyrene cassette sampling. Am. ind. Hyg. Ass. J. 52,280-286.

Siegel, S. (1956) Nonpurumetric Statistics for the Behavioral Sciences. International Student Edition, McGraw-Hill, Kogakusha.

Van Tongeren, M. J. A., Gardiner, K. and Calvert, I. A. (1994) An assessment of the weight-loss in transit of filters loaded with carbon black. Ann. occup. Hyg. 38, 319-323.