This chapter deals with fine dusting powders. Dusting powders are used to control ants, wasps, flees and crawling insects. In addition, but mainly for professional use, there are also powders that have to be dissolved or suspended in water prior to spraying. This type of product is covered in chapter 2 ‘Spray applications’.
7.1. Use and composition
Ant dusting powder
Powders to control ants are exclusively permitted for application outdoors. The dusting of a small amount of powder at the entrance to the ant nest, i.e., in crevices and between tiles and the like is preferred. If the user cannot find the nest entrance, a small amount of powder should be dusted on paths and/or along doorsteps and window frames and other places where the ants enter the house. The following is stated in one set of instructions for dusting a product: ‘Cut a corner off the inner packet using scissors, so that the contents can easily be scattered’. The active substances for ant dusting powders are deltamethrin, foxim and permethrin.
Wasp powder
Wasp powders for non-professional use are only permitted for the control of wasps outdoors. To control wasps, a small amount of powder should be put at the opening of the nest, preferably in the evening when the wasps are already in the nest. Active substances are deltamethrin and permethrin
Cat and dog fleas
To control fleas and their larvae around dogs and cats, the places where the dog and/or cat sleeps or lies down should be treated with powder. Cracks, crevices and surfaces can be treated with the insect powder. Up until April 1995 a flea powder was permitted which was sprinkled over the animals’ fur and rubbed into the skin. The current thinking is: For the effective control of fleas it is necessary to treat both the area around your cat or dog and the animal itself with a registered product designed for this purpose. Active substances in dusting powders to control fleas and their larvae are deltamethrin, permethrin and propoxur.
Crawling insects
To control crawling insects (house cricket, firebrats, carpet beetles, lice, fleas, wood lice and earwigs) in living and accommodation areas, dusting powders are permitted with permethrin and propoxur as the active substances. The directions for use indicate: ‘Use in cracks and crevices, treat the places where insects can hide; lightly dust the areas to be treated; do not use on people or pets!’
Dust mite
The directions for use indicate: ‘Sprinkle the powder over the carpet, distribute it equally over the carpet and brush the carpet with a broom, vacuum it up when it is completely dry’. The drying time is 1–3 hours; the carpet must not be walked on while it is drying. The recommendation is to check regularly, for example every 3 months in the first year and then once a year, to see whether a repeat treatment is necessary. The dosage given is: 1 packet of 750 g for 12 m2 low pile, 10 m2 middle pile and 7.5 m2 deep pile carpet. The active substance is benzylbenzoate.
Germination inhibiting products on potatoes
Germination inhibitors can be used to discourage potatoes from germinating. Germination inhibitors in powder form are permitted for non-professional users. To discourage germination, stored potatoes are dusted with the powder in the fall, before they have produced shoots. Chloroprofam is usually used as the germination inhibitor. The dosage is 500 grams per 250 kg of potatoes. It is used exclusively for potatoes for the retail market, with the understanding that the treated batches may not be consumed within 2 months after treatment.
The above-mentioned products are mainly H-products. A few powders to control fleas in the area around cats and dogs are listed under the H-products, in addition to a powder for this use listed under the V-products. The powders to control fleas in the area around cats and dogs, which fall under the H-products category, are all permitted for another application, for example the control of ants. The products that inhibit the germination of potatoes fall into the L-products category. Several of the above-mentioned products are permitted for more than one of the mentioned applications. The information about the use and composition was obtained from the Pesticide Database of the CTB (CTB, 2000a)45).
7.2. Exposure
Dusting powders can be split up into four categories:
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powders that are scattered outdoors (to control ants and wasps);
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powders used indoors to lightly dust the area to be treated. The area to be treated is the floor and/or the area where a dog or cat sleeps or lies down (to combat dog and cat fleas and against crawling insects);
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substances that have to be brushed into the carpet (against dust mite);
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germination inhibitors for potatoes.
Inhalation exposure due to evaporation
The active substances in dusting powders are all substances with an extremely low vapour pressure, and are therefore not very volatile. The inhalation exposure due to evaporation is therefore considered to be negligible. All products are fine powders that need to be scattered (for the control of ants and wasps), or with which the surface to be treated must be dusted (such as for fleas and crawling insects).
Mixing and loading
A large number of the dusting powders are supplied in a shaker, similar to an icing sugar shaker. The preparation usually involves pricking through the holes in the shaker to be able to sprinkle the contents. There are also powders that are supplied in a plastic bag, where the corner has to be cut off before the powder can be sprinkled. For the time being, it is assumed that there are no products for which the powder has to be taken out of the bag and put into a shaker. On these grounds, the exposure during mixing and loading is considered to be negligible.
Dusted surfaces and amounts used
The amount of powder that is used when controlling dust mite, according to the directions for use, is 60 to 100 g per m2 (see § 7.1). Based on this data, 2200 g is taken as the default value for the amount of powder dusted in a living room of 22 m2 (Bremmer and Van Veen, 2000)1).
The calculation of the amount of germination inhibitor on potatoes is based on the winter storage of 125 kg of potatoes. According to the directions for use, 250 g of germination inhibitor should be used. It is assumed that the storage of 125 kg of potatoes covers an area of 3 m2.
No data were found on the size of the dusted surface and the amount of dusted powder for the other applications. The dusted surfaces given in the table are estimates. It is assumed that 60 g per m2 is the amount of powder dusted per unit surface for these applications. This value is estimated based on the powder used when controlling dust mites.
Default values for dusted surfaces and amounts used
| Type of powder | Use | Dusted surface [m2] | Q | Amount of powder dusted [g] | Q |
|---|---|---|---|---|---|
| Wasp powder | Outside | 0.25 | 2 | 15 | 2 |
| Ant powder | Outside | 1 | 2 | 60 | 2 |
| Flea powder | Inside | 1 | 2 | 60 | 2 |
| Crawling insects | Inside | 1 | 2 | 60 | 2 |
| Dust mite | Inside | 22 | 4 | 2200 | 4 |
| Germination inhibitor | Inside | 3 | 3 | 250 | 3 |
Scenario
The scenario describes a non-professional user who is controlling crawling insects indoors with the help of a dusting powder. For the room in which the treatment takes place, we assume the default room given in the ‘General fact sheet’ (Bremmer and Van Veen, 2000)1) of 20 m3, 8 m2, and a ventilation rate of 0.6 hr−1. It is assumed that 60 g of powder is dusted onto 1 m2.
After application, dermal exposure can take place by a child crawling over the treated area. Oral exposure can then take place by hand-mouth contact. As the default, a child of 10.5 months who crawls over the treated area is assumed. For application indoors, it is assumed that a child is in contact with the treated area for 1 hour a day during the 14 days after application.
Exposure outdoors
A number of models have been developed in ConsExpo to describe the inhalatory exposure in a room. The spray model describes the inhalation exposure due to spraying aerosols indoors, for example, and the ‘evaporation’ model describes the exposure due to the evaporation of a substance in a room. These models can all be applied to calculate the inhalation exposure in a room. These models cannot be applied to calculate the inhalation exposure outdoors.
The dermal and the oral exposure after application outdoors can be described with the help of ConsExpo (using the ‘rubbing off’ and the ‘constant rate’ model, respectively). For application outdoors, where there is influence of sunlight, wind and rain, it is assumed that exposure occurs over a 7-day period. For outdoor application it still is assumed that the child is in contact with the treated area, for 1 hour a day.
Exposure during application
Inhalation/ oral exposure: spray model
During the dusting of the surface under treatment, the dusted particles can be breathed in and oral and/or inhalation exposure can occur. In the section above it is assumed that the evaporation of the active substance is negligible; here is mainly referred to the inhalation/oral exposure to dusted particles. When using dusting powders, the surface being treated is almost always on the ground (outdoors; ant control on the patio), the floor (indoors; fleas and crawling insects), or objects on the floor (cat or dog baskets, potatoes). An exception is the control of wasps (nests).
The parameter, which has the most influence with regard to the dispersion of particles, and therefore the exposure, is the particle size of the powder particles. In addition to the amount dusted and the duration, the sprinkling height is also of importance. The force of the wind also has to be taken into account when outdoors. Extremely fine particles can disperse with the slightest wind, and will not immediately reach the ground.
No special model, developed for the application, is available for the use of dusting powders. The use of dusting powders can be described with the help of the ‘spray’ model, which is developed for the spraying of aerosols. The definitions for a number of parameters do have to be somewhat changed. The spray model describes the behaviour of a cloud of aerosol particles, but it can also describe a cloud of solid particles, that is, a dusted powder.
‘Spray’ duration
For dusting the application duration is the ‘spray’ duration. It is estimated that it takes 5 minutes for dusting 1 m2.
Exposure duration
A total time of 4 hours is set as the default value for the exposure duration It is assumed that the user leaves the treated room 4 hours after the application.
Mass generation rate
The mass generation rate is calculated by dividing the amount of powder dusted by the duration of use. If 60 g of dusting powder is dusted in 5 minutes, the mass generation rate is 60/5 = 12 g/min.
Initial particle distribution.
The average diameter of the dusted particles should be filled in as the droplet size. The diameter of the particles is important for the time that the particles remain in the air. Smaller droplets fall more slowly. With regard to the number of particles in the air, in addition to the ‘particle size’, the ‘airborne fraction’ is also important. The airborne fraction is defined as the fraction of the particles that is dispersed in the air.
As a guideline for the size of the particles, the particle size distribution of agricultural lime is assumed. For lime marl, the legal requirement is that 99% of the lime particles are smaller than 1000 μm and 90% are smaller than 150 μm. It is provisionally defined that most of the particles will have a diameter of between 50 and 150 μm.
In the TNsG’s50) a ‘Consumer product spraying and dusting’ model is stated in which the consumer uses a hand-held dusting applicator pack for crack and crevice powders against fleas and ants. The products were found to be particles of inert filler such as fine talc or chalk (median, 45% of dust less than 75 µm)50).
Based on this data, the default value for the initial partial distribution is a lognormal distribution with a median of 75 µm and a coefficient of variation of 0.6.
Dermal exposure: constant rate
When sprinkling/dusting the surface to be treated, dermal exposure can occur, particularly of the hands. This is definitely the case for products to control dust mites, which have to be brushed into the carpet. The dermal exposure is described using the constant rate model.
Contact rate
In the above-mentioned dusting model (TNsG50)), the subjects in the study applied crack and crevice powders in a kitchen treating skirting boards, shelves and laminate surfaces. The dermal exposure on hands and forearms ranges from 0.4 to 4.18 mg/min with a 75th percentile of 2.83 mg/min. The dermal exposure for legs, feet and face ranges from 0.22 to 6.56 mg/min with a 75th percentile of 2.15 mg/min. Using these data, the default value for contact rate is set at 4.98 mg/min.
Exposure after application
Dermal exposure: ‘rubbing off’ model
Transfer-coefficient
Data about the transfer coefficient (the factor that indicates what surface is rubbed off by the skin per unit time, and is therefore transferred from the floor to the skin) is given by the EPA (1997)25). For children from 6 to 18 months who crawl over the treated carpet, a factor of 0.6 m2/hr is given, where the EPA assumes a maximum of 4 hours of activity per day.
Dislodgeable amount
The TNsG50) gives an overview of transfer efficiency for different types of surfaces, the dislodgeable amount ranges from 1% to 60%. In an HSL Pilot study on aerosols (cited in the Biocides Steering Group’s report, 19987)) 10 % is given as the value for the parameter ‘dislodgeable residue from treated carpet’. The concept-SOPs of the US-EPA25) assume that 50% of the amount of the active substance gets on to the surface. Based on this data, the default value for the dislodgeable fraction is set at 30%. The airborne fraction is taken to be 15%, so 85% of 60 g of flea powder is sprinkled onto 1 m2; the dislodgeable amount is therefore 0.85 × 60 × 0.3 =15.3 g/m2.
Oral exposure: constant rate
Ingestion rate
For the oral exposure due to hand-mouth contact, it is assumed that 10% of the amount of a product that gets onto a child’s skin is taken in orally by hand-mouth contact (see § 2.2.7). The ingestion rate can be calculated based on this assumption.
Defaults
Default values for the application of dusting powder against crawling insects, indoors
| Default value | Q | References, comments | |
|---|---|---|---|
| General | |||
| Frequency | 5 year−1 | 3 | In summer, once a month |
| Inhalation | |||
| Exposure, spray model | |||
| Spray duration | 5 min | 2 | See above |
| Exposure duration | 240 min | 3 | See above |
| Room volume | 20 m3 | 3 | Unspecified room1) |
| Room height | 2.5 m | 4 | Standard room height |
| Ventilation rate | 0.6 hr−1 | 3 | See above |
| Mass generation rate | 0.2 g/sec | 3 | Calculated, see above |
| Airborne fraction | 0.2 g/g | 1 | See § 2.2.3 |
| Weight fraction non-volatile | 1 g/g | 4 | 100% product |
| Density non-volatile | 1.8 g/ cm3 | 3 | See § 2.2.2 |
| Initial particle distribution | 75 µm (0.6) | 2 | Median (CV); see above |
| Inhalation cut-off diameter | 15 µm | See § 2.2.3 | |
| Dermal | |||
| Exposure, constant rate | |||
| Contact rate | 4.98 mg/min | 2 | See above |
| Release duration | 5 min | 2 | I.e. ‘spray’ duration |
Default values after application of dusting powder against crawling insects, indoors
| Default value | Q | References, comments | |
|---|---|---|---|
| General | |||
| Frequency | 70 year−1 | 2 | 5 × 14 days per year |
| Body weight | 8.69 kg | 4 | Child 10.5 months1) |
| Dermal | |||
| Exposure, rubbing off | |||
| Transfer coefficient | 0.6 m2 / hr | 2 | See § 2.2.6 |
| Dislodgeable amount | 15.3 g/ m2 | 2 | Calculated, see above |
| Contact time | 60 min | 2 | See above |
| Rubbed surface | 1 m2 | 2 | See above |
| Oral | |||
| Exposure, constant rate | |||
| Ingestion rate | -- | Calculated, see above | |
| Exposure time | 60 min | 2 | I.e. contact time |
