Fate of Pesticides in Surface Waters, Laboraty and Field Experiments

Fate of Pesticides in Surface Waters, Laboraty and Field Experiments

Appendix D. Experiment with filters

10.18 D.1 Introduction

In order to evaluate the usefulness of filters for separation of dissolved and sorbed pesticide, an experiment to determine the take up of pesticide by different filters was performed.

10.19 D.2 Materials

Solutions of radiolabelled pendimethalin, ioxynil and bentazone in three concentrations were used.

Pendimethalin, high concentration: 0.5 mL of 1.21 µCi/mL stock solution was added to a 50-mL measuring flask and the volume was adjusted to 50 mL with millipore water. From this, medium and low concentration solutions were prepared by diluting the high concentration 10 and 100 times with millipore water.
Ioxynil, high concentration: 2.5 mL of 0.56 µCi/mL stock solution was added to a 50-mL measuring flask and the volume was adjusted to 50 mL with millipore water. From this, medium and low concentration solutions were prepared by diluting the high concentration 10 and 100 times with millipore water.
Bentazone, high concentration: 2.5 mL of 0.50 µCi/mL stock solution was added to a 50-mL measuring flask and the volume was adjusted to 50 mL with millipore water. From this, medium and low concentration solutions were prepared by diluting the high concentration 10 and 100 times with millipore water.

Three filter types were tested:

GF-filter: Glass fibre filter, pore size of approx. 0.4 µm
CA-filter: Celluloseacetate filter, pore size of 0.2 µm
PC-filter: Polycarbonate filter, pore size of 0.22 µm

10.20 D.3 Experimental procedure

A set-up of glass filtering equipment was used. Filtering was made in this order:

Bentazone, low
Bentazone, medium
Bentazone, high
Ioxynil, low
Ioxynil, medium
Ioxynil, high
Pendimethalin, low
Pendimethalin, medium
Pendimethalin, high

For each solution, all three filter types were tested using the following procedure.

Three mL of the solution was poured through the first filter and 2 mL of the filtrate was mixed with 15 mL scintillation liquid and the activity was determined using LSC. The remaining filtrate was discarded. Using the same filter, another 3 mL was filtered and again 2 mL was collected for determination of activity. Finally, the filter was transferred to a scintillation vial and the activity was determined. A new type of filter was mounted in the equipment and the procedure was repeated. After filtering with all three filter types had been performed, the same procedure was performed with the next, stronger solution. The glass equipment was cleaned between pesticides.

For control, the same procedure was performed without filter.

10.21 D.4 Results

Table D.1

Mass balance for filtering of bentazone solutions. % relative to control

Filter	Solution	Filtrate	Filter	Total
GF-F	low concentration	91.8%	3.9%	96%
GF-F	medium concentration	93.0%	3.3%	96%
GF-F	high concentration	93.0%	2.9%	96%
CA	low concentration	96.5%	4.9%	101%
CA	medium concentration	94.9%	3.6%	98%
CA	high concentration	97.1%	4.4%	102%
PC	low concentration	99.3%	0.9%	100%
PC	medium concentration	97.7%	1.6%	99%
PC	high concentration	99.8%	1.7%	101%

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The results show that only the glass fibre filter has any potential for use for separation of sorbed and freely dissolved pendimethalin while all three types of filters can apparently be used for ioxynil and bentazone. In general, there was no difference between first and second filtering. But for pendimethalin, less pendimethalin was retained in the second filtering indicating that the filter could be saturated.