Archives of Environmental Contamination and Toxicology

, Volume 49, Issue 4, pp 577–588

Exposure to Omethoate During Stapling of Ornamental Plants in Intensive Cultivation Tunnels: Influence of Environmental Conditions on Absorption ofthe Pesticide

Authors

    • Laboratorio di Sanità Pubblica
  • L. Centi
    • Servizio Prevenzione Igiene e Sicurezza nei Luoghi di Lavoro
  • S. Santini
    • Servizio Prevenzione Igiene e Sicurezza nei Luoghi di Lavoro
  • L. Lunghini
    • Laboratorio di Sanità Pubblica
  • B. Banchi
    • Laboratorio di Sanità Pubblica
  • G. Sciarra
    • Laboratorio di Sanità Pubblica
Article

DOI: 10.1007/s00244-005-8025-2

Cite this article as:
Aprea, C., Centi, L., Santini, S. et al. Arch Environ Contam Toxicol (2005) 49: 577. doi:10.1007/s00244-005-8025-2

Abstract

This report describes a study of exposure to omethoate during manual operations with ornamental plants in two intensive cultivation tunnels (tunnel 8 and tunnel 5). Airborne concentrations of omethoate were in the range 1.48–5.36 nmol/m3. Total skin contamination in the range 329.94–12,934.46 nmol/day averaged 98.1 ± 1.1% and 99.3 ± 0.6% of the total potential dose in tunnel 8 and tunnel 5, respectively. Estimated absorbed doses during work in tunnel 5 were much higher than the acceptable daily intake of omethoate, which is 1.41 nmol/kg b.w. This finding shows that organization of the work or the protective clothing worn in tunnel 5 did not protect the workers from exposure. Urinary excretion of alkylphosphates was significantly higher than in the general population, increasing with exposure and usually showing a peak in the urine sample collected after the work shift. Urinary alkylphosphates showed a good correlation with estimated potential doses during work in tunnel 8 and are confirmed as sensitive biological indicators of exposure to phosphoric esters. The linear regression analysis between the urinary excretion of alkylphosphate, expressed as total nmol excreted in 24 h, and total cutaneous dose allows for estimating that the fraction of omethoate absorbed through the skin during work in tunnel 8 is about 16.5%.

Omethoate {O,O-dimethyl S-[2-(methylamino)-oxoethyl] phosphorothioate} is used as a systemic acaricide and insecticide on fruit trees, cereals, hops, vegetables, and ornamental plants. It has anticholinesterase activity and moderate acute toxicity with LD50  of 30 and 36 mg/kg b.w. for oral doses in rats and mice, respectively (Worting and Hance 1991). Acute toxicity of dermal doses in rats is 900 mg/kg b.w. (Worting and Hance 1991). In experiments with dietary administration to rats, a no-observed-effect level (NOEL) of 1 mg/kg of food has been reported (Worting and Hance 1991). An acceptable daily intake (ADI) of 0.0003 mg/kg b.w. (1.41 nmol/kg b.w.) has been published (WHO 1986) but occupational exposure limits are not known.

In mammals, detoxification of omethoate (OME) takes place by esterase cleavage and formation of dimethylthiophosphate (DMTP) and dimethylphosphate (DMP) (WHO 1986). These metabolites, excreted in urine as sodium or potassium salts, can be used as biological indicators of exposure to OME (Aprea et al.1994b, 2001) and to other phosphoric esters from which they may originate by cleavage of the ester group (WHO 1986). Figure 1 shows the chemical structure of OME and its breakdown products.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f1.gif
Figure 1

Chemical structure of omethoate (OME) and its breakdown products

The main aim of the present study was to evaluate exposure and occupational risk during manual operations with ornamental plants treated with omethoate in intensive cultivation tunnels. Specific aims were to evaluate inhaled and cutaneous doses and to determine their contribution to estimated total doses. A further aim was to determine the efficacy of protective clothing for reducing occupational exposure in an occupational setting different from those previously studied. Other studies of this kind have been conducted during stapling of ornamental plants in greenhouses (Aprea et al.1994b, 1999, 2002), whereas in this case stapling was carried out in tunnels and, therefore, the size of the work space, temperature, humidity, and method of working were different.

Respiratory exposure was evaluated by personal air sampling by means of fiberglass filters and amberlite XAD-2 tubes. Dermal exposure was evaluated using skin pads and hand washing. Omethoate residues on leaves were determined in order to confirm contamination of the surfaces contacting skin during re-entry after spraying and to determine the decay of active ingredient. Absorbed doses of OME were estimated from the above measures (respiratory zone concentrations and skin contamination) and from urinary excretion of alkylphosphates. GC/MS techniques were used to analyze OME in all the matrices considered, whereas GC/FPD (Aprea et al.1996a) was used to assay urinary alkylphosphates. The latter method has already been tested in studies on occupationally exposed subjects and members of the general population (Aprea et al.1994a,b, 1996b, 1997, 1998, 1999, 2001, 2005).

Materials and Methods

Subjects and Exposure Conditions

Four female workers (Nos. 1, 2, 3, 4; mean age 50 ± 6 years, range 43–55) engaged in stapling trailers of ornamental vines (Shindapsus) to a mossy support in two tunnels were monitored for a week. The tunnels (Nos. 5 and 8) had a volume of 1658 m3 and an area of 528 m2. The plants had been treated 37 h before re-entry with 220 ml FOLIMAT BAYER (565 g/L pure omethoate) dispersed in 200 L water (equivalent to 0.62 g/L of active ingredient). Treatment was done by spraying at 6 pm on Saturday and re-entry occurred the following Monday at 7 am. The daily work shift ended at 1.30 pm.

Workers 1 and 2 were occupied in tunnel 8 for all of the five days of monitoring. Workers 3 and 4 worked in tunnel 5 except on Friday, when they were sent into tunnel 8. All fixing operations were done standing, though the plants were of different heights: about 120 cm in tunnel 8 and about 150 cm in tunnel 5. Microclimatic conditions were also different in the two tunnels: relative humidity was 42 ± 3%, 38–46% (mean ± SD, range) in tunnel 8 and 66 ± 3%, 63–70% in tunnel 5; temperature was 28–30°C in both.

The four workers were in good health and had normal values of liver and kidney function parameters. Alcohol consumption was limited: less than 250 ml wine/day. Three were non-smokers, whereas no. 3 smoked 20 cigarettes per day.

Protective clothing consisted of cotton overalls with long sleeves, work shoes, and two pairs of gloves (cotton in contact with the skin and latex externally). Instead of long-sleeved overalls, workers 2 and 3 wore only salopettes. Under protective clothing, the women wore underwear, socks, and t-shirts. Work clothes were changed at least twice a week whereas the cotton gloves were changed at the discretion of the workers. Latex gloves were changed if torn or perforated. Clothes were not changed at the end of the shift (the women went home wearing the clothes they wore in the tunnels). The workers were responsible for washing their work clothes.

The working conditions reported are similar to the everyday operations performed year round during manual operations on ornamental plants in the tunnels of the studied establishment.

Environmental and Biological Monitoring

Biological monitoring was done by analysis of urinary alkylphosphates. A spot urine sample was obtained from the workers on the Monday before starting work (basal), then 24-h urine was collected in two fractions (7 am to 1.30 pm and 1.30 pm to 7 am the next day, i.e., during and after the work shift) for the rest of the working week. The samples were also used to determine urinary creatinine concentrations. The results were expressed in nmol/g creat and in total nmol excreted in the 24 h.

Personal air sampling in the respiratory zone was done throughout the working week to determine the quantity of active ingredient in inhalable airborne dust and vapor. Aerosol sampling was done on a fiberglass membrane 37 mm in diameter (Sartorius) with portable SKC samplers operating at a sampling flow of 2.9 L/min (closed face). This flow through a 7-mm aperture gave an air speed of 1.25 m/sec, the same as that of the average inspiration (Italian Law No. 277 1991). Vapors were sampled separately with amberlite XAD-2 tubes (SKC) at a sampling flow of 1 L/min, as recommended by the manufacturer. Air sampling lasted the whole work shift (6 h).

Every day of the week from Monday to Friday, deposition of OME on exposed skin (neck and head) was determined by placing a pad on the face of each worker. To assess contamination of unexposed skin, eight pads were placed on the skin under clothes in the positions shown in Table 1. The pads were squares of filter paper (49 cm2 for unexposed skin and 16 cm2 for the face) attached to the skin with sticking plaster.
Table 1

Position of pads on various parts of the body

Position of pad

Skin area represented

% of body area

Face

Head and neck

6.9

Chest

Shoulders and chest

11.4

Back

Shoulders and back

11.4

Right arm

Arms

9.7

Left forearm

Forearms

6.7

Left anterior thigh

Anterior thighs and hips

13.55

Right posterior thigh

Posterior thighs and hips

13.55

Left calf

Calves

6.75

Right shin

Ankles and feet

13.15

Skin contamination of the hands was assessed by washing: 150 ml 95 ° ethanol was slowly poured over the workers“’ hands while they rubbed them together, and collected in a disposable aluminum tray. The workers then left their hands and especially nails in the alcohol for 30 s. This procedure was carried out before breakfast and at the end of the working day (i.e., on occasions when they would normally have washed their hands). The wash liquid was poured into a personal container.

To avoid breakdown, all samples were protected from light with aluminum foil and placed in the freezer at −18°C.

Determination of Dislodgeable Foliar Residue (DFR)

To measure residues of active ingredient that could be transferred from leaves to the skin of workers, and hence the breakdown of active ingredient, leaf sampling was carried out before and immediately after spraying, then at 8 am on the five days, namely, 38, 62, 86, 110, and 134 h after treatment.

Leaf samples were obtained with a 1.5-cm-diameter punch (Iwata et al.1977). Samples each consisted of 18 discs punched from different leaves and, therefore, an area of 31.8 cm2 considering only one side of the leaf. The sampling points were the intersections of a grid dividing the two sides of the tunnel into four equal rectangles. Leaves with intermediate development were chosen.

Samples were obtained from the same leaves on Saturday, Monday, and Tuesday. On Wednesday, substitution of a number of plants made it impossible to sample the same leaves. Sampling was, therefore, conducted as described above on other plants on Wednesday, Thursday, and Friday.

The samples were protected from light with aluminum foil and frozen at −18°C until analysis.

Analysis of Samples

Urine

Alkylphosphates were analyzed by gas chromatography with flame photometric detection (FPD) after derivatization with pentafluorobenzylbromide (Aprea et al.1996a).

Fiberglass filters and pads

Samples were spiked with chlorpyrifos methyl as internal standard, dried for 60 min, and extracted with three 10-ml portions of acetone in a mechanical shaker. Pooled extracts were evaporated to dryness in a rotary evaporator at 30°C. The residue, made up with 0.5 ml toluene, was injected into the GC/MS.

XAD-2 tubes

The adsorbent phase, spiked with chlorpyrifos-methyl as internal standard, was dried for 60 min. The sample was then kept in contact with 5 ml toluene for 30 min before analysis by GC/MS (NIOSH 1994).

Hand wash liquid

10-ml sample, spiked with chlorpyrifos-methyl as internal standard, was evaporated to dryness in a rotary evaporator at 30°C. The residue, made up with 1 ml toluene, was injected into the GC/MS.

Leaves

DFR was obtained washing samples twice with 25 ml of 0.01% solution of sodium dioctyl sulfosuccinate and then with 25 ml water. Pooled wash solution spiked with chlorpyrifos-methyl as internal standard, was extracted three times with 30 ml dichloromethane. Pooled extracts were dehydrated with anhydrous sodium sulfate and evaporated to dryness in a rotary evaporator at 30°C. The residue, made up with 1 ml toluene, was analyzed by GC/MS.

Reproducibility, recovery, and detection limits of the analytical procedures are shown in Table 2.
Table 2

Detection limits (DL), precision (RSD%), and recovery of analyses for environmental and biological monitoring

Sample

DLa

Conc.

No. replicates

Precision within series (RSD%)b

Precision between series (RSD%)b

Mean recovery (%)b

XAD-2 tubes (μg/sample)

0.050

Fiberglass filters (μg/sample)

0.010

0.735 2.939

10 10

9.8 9.4

9.3 9.7

84 101

Pads 16 cm2 (μg/sample)

0.024

0.735 2.939

10 10

8.2 9.1

10.1 12.4

90 98

Pads 49 cm2 (μg/sample)

0.024

0.735 2.939

10 10

7.4 7.5

11.5 11.9

92 96

Hand wash (μg/10 ml)

0.007

Leaves (μg/sample)

0.100

a DL was calculated on the basis of a signal three times that of background noise for an ion with m/z 156.

b — = Precision and recovery were not evaluated.

Calculation of Exposure Doses

Pesticide concentrations in air were used to calculate actual respiratory dose, assuming a lung ventilation of 15 L/min (Zhuang et al.1993).

Daily skin contamination (excluding hands) of each worker was taken as the sum of contamination of the various anatomical regions represented by the pads placed on them. Contamination of each region was obtained by multiplying the concentrations detected in pads (nmol/cm2) by the surface area of the skin represented, the percentages of total body area of which are shown in Table 1 (Popendorf and Leffingwell 1982; Davis 1980). Total body area was calculated for each worker with the formula of Du Bois (Du Bois and Du Bois 1916). The sum of hand contamination (the quantity of omethoate found in hand wash liquid) and contamination of other parts of the body was the total daily skin contamination. To calculate absorbed doses, 10% skin penetration (Brouwer et al.1992; Byers et al.1992) and 100% lung retention (Brouwer et al.1992; Stephanou and Zourari 1989; Fenske and Elkner 1990) were assumed.

Statistical Analysis

Statistical analysis was carried out using the Stat View statistical package.

Results

Figure 2 shows DFR of OME immediately before and after spraying and on subsequent working days. With our data, it was not possible to accurately estimate breakdown kinetics because sampling was done on the same leaves only on Saturday, Monday, and Tuesday and on Wednesday, Thursday, and Friday. In the last three days, decay was linear in both tunnels with an angular coefficient of −0.017 in tunnel 8 and −0.015 in tunnel 5. This means that:
$${\rm DFR} ({\rm nmol}/{\rm cm}^{2}) = - 0.017(-0.015) \cdot {{ {\rm h} + {\rm a}}} $$
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f2.gif
Figure 2

DFR of omethoate immediately before and after spraying and on subsequent working days

where “h” “is time since spraying and “a” is the intercept that depends on the initial concentration of the pesticide on leaves.

Table 3 shows omethoate concentrations in personal air samples and pads, as well as the quantities of active ingredient in hand wash liquid of workers during the working week monitored. In general, the concentration of pesticide in inhalable airborne particulate ranged from 1.48 to 5.36 nmol/m3, whereas in the vapor phase it was always below the analytical detection limit. Quantities found in hand wash liquid were between 17.07 and 341.9 nmol, whereas in face pads (representing exposed skin of the head and face) they were between 3.518 and 35.47 pmol/cm2.
Table 3

Exposure data for four female workers during the working week monitored

Sample

Mean ± SD

Median

Geometric mean

Range

Personal air samples (nmol/m3)

    

  All data (N = 20)

2.40 ± 0.906

2.17

2.27

1.48–5.36

  Tunnel 5 (N = 8)

2.28 ± 0.636

2.17

2.21

1.60–3.28

  Tunnel 8 (N = 12)

2.47 ± 1.07

2.24

2.31

1.48–536

Hand wash liquid (nmol)

    

  All data (N = 20)

83.80 ± 83.86

53.75

59.28

17.07–341.9

  Tunnel 5 (N = 8)

129.4 ± 1123

65.67

93.02

28.05–341.9

  Tunnel 8 (N = 12)

53.42 ± 40.12

43.11

43.90

17.07–162.9

Face pads (pmol/cm2)

    

  All data (N = 20)

17.99 ± 9.087

18.03

15.31

3.518–35.47

  Tunnel 5 (N = 8)

17.74 ± 9.027

16.56

15.07

3.518–29.61

  Tunnel 8 (N = 12)

18.15 ± 9.523

19.35

15.47

5.863–35.47

Unexposed skin pads (pmo/cm2)

    

  All data (N = 150)

227.3 ± 1068

18.43

23.41

1.149–10320

  Tunnel 5 (N = 58)

488.9 ± 1682

17.28

32.31

1.149–10320

  Tunnel 8 (N = 92)

62.29 ± 160.5

19.10

19.11

1.149–1383

With regard to pads on skin covered by clothing, Table 3 shows a wide interval of variation over four orders of magnitude. It is worth recalling that two workers, no. 3 in tunnel 5 and no. 2 in tunnel 8, did not wear long-sleeved overalls. Their forearms and part of the upper arm were bare, which probably explains the extremely high variability of this data.

Different areas of skin were found to have different contamination levels (Table 4). Taking the data as a whole, higher pesticide concentrations were detected on forearms, arms, and anterior thigh with the following ranges: 21.25–10,320 nmol/cm2, 1.149–744.5 nmol/cm2, and 8.136–1009 nmol/cm2, respectively. Means in these areas of unexposed skin were much higher than those indicated by face pads (range 3.518–35.47 nmol/cm2), a part of the body not protected by clothing. Table 4 also shows that the posterior parts of the body (back and posterior thigh) were less contaminated than the corresponding anterior parts, and that inferior parts of the body such as the calf and shin were always contaminated to a significant degree. The back was the least contaminated part, probably due to the fact that workers wore a t-shirt under their overalls and moreover because occasions for contact with the back were few. Contamination of unexposed skin was, therefore, concentrated in certain areas and the Kruskal-Wallis test (non-parametric ANOVA) showed that pad position was a significant variable (p < 0.0001) for contamination of skin protected by clothing.
Table 4

Contamination of various skin areas of four female workers during the working week monitored

Sample

Mean ± SD

Median

Geometric mean

Range

Back pads (pmol/cm2)

    

  All data (N = 20)

12.45 ± 26.26

2.967

4.041

1.149–101.4

  Tunnel 5 (N = 8)

16.52 ± 3439

5.217

5.178

1.149–101.4

  Tunnel 8 (N = 12)

9.732 ± 20.45

2.680

3.425

1.149–73.42

Chest pads (pmol/cm2)

    

  All data (N = 20)

40.18 ± 100.9

10.53

12.29

2.393–452.4

  Tunnel 5 (N = 8)

86.25 ± 153.4

27.14

26.07

4.499–452.4

  Tunnel 8 (N = 12)

9.469 ± 6.494

6.509

7.439

2.393–20.96

Calf pads (pmol/cm2)

    

  All data (N = 19)

22.62 ± 16.72

18.76

15.49

2.297–53.41

  Tunnel 5 (N = 7)

5.798 ± 2.900

6.222

5.082

2.297–9.572

  Tunnel 8 (N = 12)

32.43 ± 12.95

32.98

29.67

12.73–53.41

Posterior thigh pads (pmol/cm2)

    

  All data (N = 16)

22.42 ± 37.52

11.77

11.33

1.149–155.2

  Tunnel 5 (N = 6)

32.18 ± 60.43

7.275

10.87

3.255–155.2

  Tunnel 8 (N = 10)

16.56 ± 14.69

12.59

11.62

1.149–54.47

Shin pads (pmol/cm2)

    

  All data(N = 15)

20.50 ± 11.24

20.87

16.99

4.116–38.58

  Tunnel 5 (N = 5)

15.30 ± 8.42

18.09

12.79

4.116–23.93

  Tunnel 8 (N = 10)

23.11 ± 11.93

22.26

19.59

4.595–38.58

Anterior thigh pads (pmol/cm2)

    

  All data (N = 20)

166.6 ± 255.5

91.94

74.90

8.136–1009

  Tunnel 5 (N = 8)

282.7 ± 386.6

37.24

73.32

8.902–1009

  Tunnel 8 (N = 12)

89.13 ± 36.00

98.74

75.98

8.136–154.0

Arm pads (pmol/cm2)

    

  All data (N = 20)

90.84 ± 194.3

15.08

20.42

1.149–744.5

  Tunnel 5 (N = 8)

148.0 ± 244.3

74.28

67.21

10.91–744.5

  Tunnel 8 (N = 12)

52.75 ± 152.7

8.663

9.228

1.149–537.1

Forearm pads (pmol/cm2)

    

  All data (N = 20)

1340 ± 2704

229.8

311.6

21.25–10320

  Tunnel 5 (N = 8)

2972 ± 3814

654.9

1078

140.0–10320

  Tunnel 8 (N = 12)

251.0 ± 371.0

147.6

136.2

21.25–1383

Concentrations detected in face pads did not seem to show a statistically significant correlation with those of inhalable airborne particulate, suggesting that different modes of deposition determined contamination of exposed skin. A possibility could be accidental contact of the face with contaminated hands and/or clothes or surfaces.

Similarly, the quantities of omethoate detected in hand wash liquid did not show correlations with concentrations on leaves during the working week. This may be because hand contamination depended more on incorrect or non-constant use of gloves than on penetration of gloves by pesticide.

Tables 3 and 4 also show respiratory and cutaneous exposure levels in the two tunnels. It is interesting that while omethoate levels in face pads were similar in the two tunnels, contamination of hands and certain skin areas was higher in tunnel 5, and the other way round for other skin areas. The results for chest in tunnel 5 and calf in tunnel 8 stood out. An explanation could be a relation with the size of the plants handled: a height of 150 cm in tunnel 5 involves contact with leaves at chest and neck level of the women who were 154 and 162 cm tall. On the other hand, in tunnel 8, lower parts of the body (shin and calf) were comparatively more contaminated, possibly due to brushing against the lower foliage in that case.

Estimated actual and absorbed doses are summarized in Table 5.
Table 5

Estimated respiratory and cutaneous doses of omethoate for four female workers during the working week monitored

 

Respiratory dose (nmol)

Cutaneous dose (nmol)

Actual total dose (nmol/kg b.w.)

Total absorbed dose (μg/kg b.w.)

All data (N = 20)

    

  Mean ± SD

12.62 ± 4.95

2236.2 ± 3260.2

40.37 ± 63.94

4.23 ± 6.41

  Median

11.17

809.61

12.24

1.51

  GM

11.90

1166.7

19.64

2.21

  Range

8.033–28.95

329.94–12934

6.380–253.9

0.745–25.7

Tunnel 5 (N = 8)

    

  Mean ± SD

11.60 ± 3.21

4273.7 ± 4507.4

82.56 ± 87.46

8.46 ± 8.78

  Median

11.17

2358.1

46.52

4.90

  GM

11.23

2357.4

45.67

4.85

  Range

8.033–16.89

589.41–12934

11.27–253.9

1.26–25.7

Tunnel 8 (N = 12)

    

  Mean ± SD

13.30 ± 5.879

877.91 ± 631.17

12.24 ± 5.897

1.42 ± 0.612

  Median

11.92

632.77

10.88

1.19

  GM

12.37

729.95

11.19

1.31

  Range

8.190–8.95

329.94–2506.9

6.380–26.85

0.745–2.84

Under our working conditions, respiratory dose was much lower than skin contamination, being [mean ± SD (range)] 1.9 ± 1.1 (0.66–4.3)% and 0.71 ± 0.57 (0.12–1.5)% of the total dose in tunnel 8 and tunnel 5, respectively. For estimated absorbed doses, the respiratory percentages were [mean ± SD (range)] 16 ± 7.8 (6.2–31)% and 6.4 ± 5.0 (1.2–13)% of the total in tunnels 8 and 5, respectively. The percentages of the total skin contamination contributed by hands, exposed skin (face and neck), and unexposed skin were [mean ± SD (range)] 9.9 ± 13 (0.78–49), 2.8 ± 1.2 (0.93–4.7), and 87 ± 13 (48–97) in tunnel 8 and 7.9 ± 11 (0.43–35), 1.2 ± 1.6 (0.24–4.6), and 91 ± 13 (61–99) in tunnel 5. The main contribution to cutaneous dose was from hand contamination and contamination of skin covered by clothes. Analysis of the data showed that respiratory intake and face and neck contamination were a higher percentage of the total in tunnel 8 than in tunnel 5 and the difference was statistically significant. The percentage contribution of hands was not statistically significant.

Figure 3 shows the mean percentage contamination in different parts of the body with respect to the dose detected on unexposed skin. In general, the thighs, anterior hips, and forearms were the skin areas contributing most to the total dose in both tunnels. This finding is in line with the results of pad analysis on forearms but not on thighs and hips. Indeed, the latter area made a preponderant contribution not due to the high concentration of pesticide but for the large area of this part of the body. Contamination of this area is not only presumably due to actual contact of clothes with plants, but also to secondary contamination that may occur during visits to the toilet. The first observation is confirmed by the fact that the percentage was greater in tunnel 8. As observed in Tables 3 and 4, the chest contributed a greater proportion in tunnel 5, whereas the lower parts of the body made a higher percentage contribution in tunnel 8. Another interesting finding was that forearms contributed a greater percentage in tunnel 5, where transfer of plants required greater effort and greater use of this part of the body associated with a greater possibility of contamination by brushing against plants.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f3.gif
Figure 3

Mean percentage contamination in different parts of the body with respect to the dose detected on unexposed skin

Comparison of absorbed doses estimated from exposure data with ADI are reported in Figure 4, where careful inspection shows that absorbed doses were up to 18 times ADI only in workers 3 and 4 during work in tunnel 5. For those working in the other tunnel, maximum values observed were double the ADI.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f4.gif
Fig. 4

Absorbed doses and ADI. White histograms represent data from tunnel 5. Absorbed doses were estimated from exposure data

Alkylphosphate concentrations of the four workers are shown in relation to the geometric mean of the general population (Aprea et al.1996b) in Figures 5 and 6.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f5.gif
Fig. 5

Urinary excretion of alkylphosphates during the week of monitoring (tunnel 8)

https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f6.gif
Figure 6

Urinary excretion of alkylphosphates during the week of monitoring (tunnel 5 every day except Friday when the worker was in tunnel 8)

The values were on the whole low though significantly higher (Mann–Whitney U test: α = 0.05 than in a group of the general Tuscan population not occupationally exposed to pesticides (124 subjects) in whom concentrations of DMP + DMTP had a geometric mean of 126.9 nmol/g creat (Aprea et al.1996b). With few exceptions, peak excretion occurred in the 17 h after the work shift. Worker 2 showed anomalous values, with a maximum during working hours on the Monday.

Plotting the urinary excretion of alkylphosphates by the four workers in nmol/h (clearance), we obtained the graph of Figure 7, which shows that the velocity of excretion was greatest in the sample obtained “after work.”
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f7.gif
Figure 7

Urinary excretion of alkylphosphates by the four workers during the working week monitored

During work in tunnel 8, urinary excretion of alkylphosphates, expressed as total nmol excreted in 24 h, showed a significant correlation in a multiple regression model with respiratory dose and total cutaneous dose (R2 = 83.6%, p = 0.0003). The model (Table 6) showed that all parameters of the equation were significant, with cutaneous dose emerging preponderantly and positively, whereas the coefficient for respiratory dose was negative.
Table 6

Multiple regression model between urinary excretion of alkylphosphates and doses estimated from exposure dataa

\( {\rm{Equation: DMP}} + {\rm{DMTP (nmol/24h)}} = 7.848{\rm X}_{1} + 0.178{\rm{X}}_{2} + 141.142 \)

Significance (p)

Intercept

0.0113

X1 = respiratory dose (nmol)

0.0241

X2 = cutaneous dose (nmol)

0.0001

a Data obtained during the work shift in tunnel 8 (n = 12).

The model was not significant when the data of tunnel 5 were also inserted in the previous regression, nor when the data of tunnel 5 were considered alone.

Since cutaneous dose was the one that best described the biological monitoring data, both quantitatively and qualitatively, we performed a linear regression between the urinary excretion of alkylphosphate data, expressed as total nmol excreted in 24 h, and total cutaneous dose. The trend of the regression is shown in Figure 8. The variance explained by the model, 70.2%, confirmed the importance of skin exposure in determining absorption of omethoate during the occupational task investigated. The same regression performed inserting total dose instead of cutaneous dose, did not show significant changes in the equation or in significance levels, confirming the minor importance of respiratory exposure (y = 46.939 + 0.164x, r2 = 0.696, p = 0.0007).
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f8.gif
Figure 8

Linear regression between urinary excretion of alkylphosphates and skin dose estimated during work in tunnel 8 (y = 48.286 + 0.165x, r2 = 0.702, p = 0.0007)

It is possible to estimate the fraction of omethoate absorbed through the skin during work in tunnel 8 from Figure 8: The angular coefficient of the line suggests a mean absorption of 16.5%. The intercept of the regression performed inserting total dose instead of cutaneous dose (46.939 nmol/24 h) should indicate the level of alkylphosphates in urine, not associated with occupational exposure.

Calculation of absorbed doses from the biological monitoring data (nmol of DMP + DMTP excreted in 24 h minus 46.939, the presumed mean basal level in the case of non-exposure), we obtained the results shown in Figure 9.
https://static-content.springer.com/image/art%3A10.1007%2Fs00244-005-8025-2/MediaObjects/244_2005_8025_f9.gif
Figure 9

Comparison of absorbed doses obtained from environmental data and from biological monitoring data and comparison with ADI

Figure 9 reveals some important aspects of the occupational activity carried on in tunnel 5:

  • In the case of worker No. 3 whose clothing had short sleeves, estimates based on environmental data on the first day of re-entry (Monday) were much higher than those estimated from biological data. On the other hand, on day 3 (Wednesday), estimates from environmental data were much lower than those obtained from biological data.

  • In the case of worker No. 4 who wore long-sleeved overalls, estimates from environmental data on the first day were higher than those estimated from biological data, whereas the opposite was observed on days 2, 3, and 4.

  • This discrepancy, which was only observed in tunnel 5, could be ascribed to the method used to evaluate skin contamination. The technique of pads gives reliable data only if there is homogeneous deposition of the contaminant on the part of the body represented by the pad. If contamination is not homogeneous, the pad, being small, cannot correctly represent the whole skin area. This is probably what happened on the first day of re-entry, when the pad method presumably overestimated skin contamination.

There is another important aspect to examine in order to understand the striking differences found between work done in the two tunnels. These differences are also documented by the results of ANOVA on all the data (except data of day 1 in tunnel 5) with urinary excretion of alkylphosphates in nmol/24 h as dependent variable, the tunnel as factor, and total potential dose in nmol/kg b.w. as covariate. The model indicates both variables as significant (p = 0.0229 and 0.0362, respectively) but the tunnel alone explained 24% of the variance of the data as compared with 20% explained by potential dose. We, therefore, asked what differences there were between the two tunnels. Apart from the height of the plants handled, which has already been discussed, it is necessary to consider the different relative humidities. The influence of humidity in determining absorption was, therefore, deduced indirectly from differences observed between tunnels.

Discussion

The methods of sampling airborne omethoate (particulate and vapor) were previously used by the authors in similar occupational situations (Aprea et al.1994b, 2001). Evaluation of cutaneous exposure by filter paper pads and hand washing with 95% ethanol has also been described in other studies (Aprea et al.1994b, 1999, 2001, 2002, 2005). Alcohol and other organic solvents can alter the barrier properties of the skin, thus increasing the potential for pesticide absorption following subsequent exposures between two washes (van Hemmen and Brouwer 1995). This is a negligible problem in this study because the daily work shift ended at 1:30 pm and the washing procedure was carried out only one time during the work (before breakfast at about 9:30 am).

The sample extraction methods used are rapid and give good recovery of analyte and good precision within and between series. The gas chromatographic analysis with mass detection is sufficiently specific not to require purification of extracts. The detection limits are low enough to enable detection of analyte in all environmental samples, even under low exposure conditions such as those observed in the present study. The conditions of sample conservation used ensure good stability of the active ingredient in all matrices for 30 days, the time necessary to carry out all the analyses.

Evaluation of personal respiratory exposure to omethoate was carried out for airborne particulate and for vapor because a vapor pressure of 3.3 mPa at 20°C (Worting and Hance 1991) did not enable us to exclude the presence of this form in the work environment. The sum of particulate and vapor recorded during the week of monitoring were similar to those reported in previous studies: during stapling of ornamental plants (Shindapsus) in greenhouses, omethoate was found in concentrations of 2.3 ± 0.7 nmol/m3, 1.5–3.1 nmol/m3 (mean ± SD, range) on the first day of re-entry (Aprea et al.1994b) and personal exposure was in the range 1.2–4.5 nmol/m3 during various manual operations (positioning, spacing, selection, and watering) in greenhouses in which the same pesticide was used (Aprea et al.2001).

In the present study, skin contamination was evaluated by a modification of the conventional pad technique proposed by Durham and Wolfe in 1961 (Durham and Wolfe 1961). Pads on various areas of exposed and unexposed skin were considered representative of the corresponding parts of the body on which contamination was assumed to be homogeneous.

Airborne pesticide as aerosol is a source of respiratory exposure and skin contamination of parts of the body not covered by clothing. The concentration of omethoate measured on face pads did not, however, show a significant correlation with that in personal air samples, presumably due to the fact that contamination of exposed skin may be attributed to both deposition of airborne particulate and contact with contaminated hands and/or clothes. The present results (range 3.518–35.47 pmol/cm2) are on the whole lower than those observed during various manual operations (positioning, spacing, selection, and watering) in greenhouses treated with the same pesticide in which the range of variation was 19.2–127.1 pmol/cm2 (Aprea et al.2001).

Hands were regularly contaminated with omethoate and the levels recorded are probably due to contamination of the inside of gloves. The present results (mean ± SD = 83.80 ± 83.86 nmol; range = 17.07–341.9 nmol) were similar to those reported in previous studies: during stapling of ornamental plants (Shindapsus) in greenhouses, omethoate was recorded at levels of 65.3 ± 19.0 nmol, 39.9–8.40 nmol (mean ± SD, range) on the first day of re-entry (Aprea et al.1994b). The present levels were much lower than those encountered during manual operations in greenhouses treated with omethoate, hand contamination being in the range 11.0–40712.9 nmol (Aprea et al.2001).

With regard to pads placed on unexposed skin, contamination may be due to incomplete closure of overalls at the neck, rolling up of sleeves, wearing of sleeveless or short-sleeved garments, entry of pesticide through open parts such as trouser legs, sleeve cuffs, and collar, and by penetration through the fabric or through joins such as seams and zips. Perusal of the results showed that in certain cases, heavy contamination observed especially during work in tunnel 5 was probably due to exposure of areas of skin such as forearms (rolled-up sleeves and sleeveless garments). In all other cases, contamination may be due to penetration through the fabric. As already observed, the height of the plants handled could be the cause of variations in contamination of skin areas in the two tunnels. Concentrations of omethoate on pads placed on the chest varied in the range 2.393–452.4 pmol/cm2 and was much higher than those recorded during stapling of small ornamental plants in greenhouses treated with the same active ingredient (4–7 pmol/cm2) (Aprea et al.1994b). The concentrations found on all pads on unexposed skin (1.149–10320 pmol/cm2) were even higher than those reported during manual operations in greenhouses treated with omethoate in which variations were in the range 19.2–250.6 nmol (Aprea et al.2001).

In the present study, on the average, the respiratory dose was only a small percentage of the total dose (1.9 ± 1.1% and 0.71 ± 0.57% in tunnel 8 and tunnel 5, respectively). These values are in the ranges observed during manual tasks in greenhouses treated with omethoate, in which the mean percentages were 16.2%, 3.8%, 3.4%, and 0.0% during spacing, positioning, selection, and watering, respectively (Aprea et al.2001).

On the average, skin dose was composed of about 9% from hand contamination, 2% from exposed skin, and 89% from unexposed skin. These findings are quite different from those reported during manual tasks in greenhouses treated with omethoate, in which hand contamination averaged 51%, 28%, 75%, and 79% during spacing, positioning, selection, and watering, respectively, whereas unexposed skin averaged 0.0%, 27%, 16%, and 15% for the same tasks (Aprea et al.2001).

With regard to this type of contamination, the part of the body contributing most to the total was the forearms (59.2% and 32.4% for tunnels 5 and 8, respectively) followed by thighs and anterior hips (18.1% and 32.1% for tunnels 5 and 8, respectively). The reason for the high contribution of forearms is straightforward, whereas that of thighs and anterior hips is probably due to contamination by dirty hands and clothes when overalls were lowered in the toilet and due to contact of this area of the clothing with plants while on the job. This observation was confirmed in previous studies carried out during stapling of ornamental plants treated with chlorothalonil (Aprea et al.2002).

Estimated absorbed doses of omethoate were compared with the ADI of 1.41 nmol/kg b.w., which is the quantity of pesticide that can be absorbed daily over a lifetime without manifesting toxic effects. Although the ADI is calculated for the general population, which is exposed through residues in food, it is often used as a reference, below which occupational risk is presumed to be negligible. The present absorbed doses estimated from respiratory and cutaneous exposure data (assessments external to the body), expressed in nmol/kg b.w., were similar or slightly higher than ADI on all days of monitoring in tunnel 8. On the other hand, in tunnel 5, maximum values about 18 times ADI were recorded. Even higher values were obtained in certain cases in tunnel 5 when estimates were based on biological data. This finding shows that organization of the work or the protective clothing worn in tunnel 5 did not protect the workers from exposure. One reason for the differences between the two tunnels may be the different relative humidities: an average relative humidity over 65% in tunnel 5 may cause greater skin absorption than the average of 16.5% estimated in tunnel 8. Results with other pesticides confirm this hypothesis: cutaneous application of propoxur at relative humidities of 50 and 90% (cutaneous humidity of 17 and 40%) results in absorptions of 13 and 63%, respectively (Meuling et al.1997).

Urinary excretion of alkylphosphates expressed in nmol/g creat was significantly higher than in the general population not occupationally exposed to pesticides in whom excretion of metabolites is probably derived from organophosphate residues in food and drinks. In most cases, the greatest concentration of metabolites was encountered in the urine samples passed between the end of one work shift and the beginning of the next (after work sample). The peak of excretion in the urine sample collected in the 17-h period between the end of one shift and the beginning of the shift on the following day is confirmed by the clearance of metabolites expressed in nmol/h.

The biological monitoring data recorded in the present study varied in the range 8.38–854 nmol/g creat in tunnel 8 and 38.3–2496 nmol/g creat in tunnel 5, and was higher than that observed in previous studies. During various manual tasks in greenhouses treated with omethoate, fenitrothion, and tolclofos-methyl, urinary excretion of DMP + DMTP varied in the range 59.8–334.7 nmol/g creat (Aprea et al.2001). During stapling of ornamental plants in greenhouses treated with omethoate, urinary excretion of the same metabolites varied in the interval 57.0–205 nmol/g creat (Aprea et al. 1994b). During stapling of ornamental plants in greenhouses treated with fenitrothion, the range was 80.0–629.9 nmol/g creat (Aprea et al.1999). The biological data, therefore, confirmed the exposure data, and as far as work in tunnel 8 is concerned, also showed a good correlation with respiratory and cutaneous exposure data. The percentage of skin penetration that best describes the urinary excretion data during work in tunnel 8 is 16.5%. This is based on the assumption that metabolic pathways other than formation of methylated alkylphosphates (DMP and DMTP) were negligible for omethoate and that the metabolites were, therefore, in a 1:1 molar ratio with omethoate absorbed.

Conclusions

The present study reveals non-negligible exposure levels for workers during stapling of ornamental plants previously treated with omethoate in tunnels. Absorbed doses, estimated from cutaneous and respiratory exposure data and from biological monitoring data, were higher than ADI, especially for the women working in tunnel 5.

Since cutaneous doses were much higher than respiratory doses, measures are needed to reduce contamination, especially under conditions of high relative humidity, which facilitate transcutaneous absorption. The contamination of unexposed skin suggests that the protective clothing was inadequate or incorrectly worn. Further work is underway on these problems, including use of different kinds of gloves and garments and different work practices.

The good correlation found between urinary excretion of alklyphosphates and cutaneous doses during work in tunnel 8 suggests that average skin penetration was 16.5% at 42% relative humidity. Alkylphosphates were confirmed as good indicators of exposure to organophorsphoric esters at exposure levels well below those associated with toxic effects.

The significant results of this study can be extended to other situations in which similar protective clothing was worn and a similar re-entry time after spraying with omethoate at the same dose was used.

Copyright information

© Springer Science+Business Media, Inc. 2005