Other FOCUSsw Calculations
A.
CALCULATING PECSW FOR FORMULATION -ANNEX I /
ZONAL APPLICATION:
For formulation, we only consider spray drift, not drainage or run-off. Only
the initial PECsw is calculated for a single application of formulation, not
multiple applications, or later time points.
Reason: it is considered that after application all components of a product
will behave independently, dissipating at different rates. (There is also not
usually information available on degradation of the formulation).
Use the FOCUS drift calculator in SWASH to determine a nominal
concentration due to spray drift, using the application rate expressed as
product, adjusted for the specific gravity of product, as described below.
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Open SWASH.
Click on ‘Information’ tab
Click on 2nd button down ‘Drift’ to open the drift calculator.
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Enter application rate. [Rate of the product not active substance e.g.
L product/ha. Multiply this by the density of the formulation
(g/cm3) to get the weight of applied formulation as kg/ha, as 1 Litre
weighs 1 kg. Enter this as the application rate in g/ha.]
Enter number of applications as 1.
Choose crop as appropriate from drop down menu.
Leave ‘Use Focus’ box as ‘FOCUS values’. (The drop down menu
here allows this to be changed to buffer zone distances if required).
Select each water body (ditch, stream, pond) in turn and for each
note the nominal concentration (µg/l) in water resulting from drift
event. (No need to multiply the stream nominal concentration by
1.2 for the upstream catchment in this case, as the formulation in the
upstream section can be assumed to have broken down into
constituent parts by the time it reaches the ‘edge of field’ stream. i.e.
the same reason we don’t consider multiple applications for
formulation).
For the stream, multiply this concentration by 1.2 to account for the
additional 20% treated upstream catchment associated with this
water body.
Use these values as your PECsw concentrations for formulated
product.
B.
PSEUDO PECSW (FOR SEDIMENT DWELLERS STUDY
DOSED IN WATER LAYER)
Where a sediment dwellers study has been spiked in the overlying water
instead of the sediment, a pseudo PECsw value may be needed by
ecotoxicology rather than a PECsed value. The way to do this in FOCUS
SW is to use the outputs from the FOCUS SW STEP 1 and 2 Report. Take
the total loading (mg/m2) into the water body from drift and from run-off /
drainage and sum them together.
Convert these to a water concentration by multiplying by 3.32, (a conversion
factor of mg/m2 to µg/l for a static 30 cm deep water body). Compare these
to the RAC value.
If this fails the risk assessment, compare the ecotoxicology endpoint based
on the dose applied to the water phase of the sediment-dwelling organisms
study against the maximum STEP 3 PECsw concentrations.