Potato Treatment
Operator Exposure & Chemical run-off Study

Procedure

4. Spinning disc and hydraulic applicators housed in this cabinet.  Note contamination on side of table resulting from operation of spinning disc applicator.

3. Microstat in operation

2. Sampling during operation of Microstat. Note positions of air sampling equipment and drip tray.  Operator remained with each applicator throughout the trial.

1. General arrangement

Results

Ratio = Results referenced to Microstat

A,B,C,D,E = Sample positions – See diagram.
Average = average value of A,B,C,D,E.
Ratio = Average values referenced to Microstat.

Date of study   27th March 1991

Place        Covered storage area, Potato Marketing Board - Sutton Bridge
Applicators        Microstat, Spinning Disc, Conventional Hydraulic Sprayer
Potato Size        <45 mm diameter
Treatment            Storite (Thiabendazole 45% w/v)
Treatment Rate           Nominally 6 tonnes per hour.  Actually 4tph for Microstat and Spinning Disc, 6tph for hydraulic.
Application Rate           90 ml Storite per tonne (40g thiabendazole per tonne)
Dilution Rate

Microstat                    - 90 ml Storite to 270 ml with water

Spinning Disc            - 90 ml Storite to 270 ml with water

Hydraulic                    - 90 ml Storite to 1600 ml with water

Sample Time          60 minutes each applicator
Sample Method          Air drawn through a glass fibre filter (Whatman GFA 37 mm diameter) held in a plastic open face filter holder at 2 litres per minute. Note - A 25 mm diameter filter held in 7 hole protected face filter holder is the type recommended for atmospheric sampling of total inhalable particulates by the HSE.  The reason for not using this type of holder was that they are made from aluminium and may have affected the sampling of particulates that are electrostatically charged.
Sample Pump            Casella AFC 123is
Sampling Method            Run-off Material collected on the tray over the sampling time was washed into a 2.5 litre container with water.
Tray Size          0.8 m x 1.22 m (0.976 m²)
Analytical Method            See attached method
Date of Analysis             11th April 1991
Sample Preparation           The filters were removed from their holders immediately after sampling and placed in an amber glass screw cap vial.  Samples were stored in the dark at 4^oC until 11/4/91.  The filters were treated with 5.0 ml methanol and analysed as described in the attached method.
Sample Preparation - run-of        The material collected in the tray was washed into a 2.5 litre container with water.  The samples were stored in the dark at room temperature until 11/4/91.     Each sample was mixed thoroughly and 1.0 ml diluted to 50.0 ml with methanol for analysis as per filter extracts above.
Occupational Exposure Limit            Thiabendazole 5 mg/m³ (8-hour TWA value) (RP)

Appendix

A study was conducted to determine the concentration of thiabendazole in the atmosphere, and the quantity of chemical run-off, resulting from the treatment of potatoes with three types of applicator.  The applicators used were the Microstat, Mantis (conventional spinning disc applicator) and a conventional hydraulic sprayer.  Atmospheric samples were taken from four points around each applicator, and from the breathing zone of the applicator operator.  The run-off from each applicator was collected in a tray positioned below the roller table.

 The results indicate that the Microstat produces significantly less atmospheric contamination and chemical run-off than the other applicators.

Each applicator was used in turn for one hour to treat potatoes at a nominal rate of 6 tonnes per hour.  Storite, a formulation containing 45% w/v thiabendazole, was applied at the rate of 90 ml per tonne (40g thiabendazole per tonne). Four area samples were taken 1 m from, the centre of each applicator. A fifth sample was taken from the breathing zone of the applicator operator. See diagram below for positions.

 The chemical run-off was collected in a tray under the roller table directly below each applicator.  The tray area was slightly larger than the base of each applicator in order to collect the direct chemical run-off.