05.01.2013 Views

technical guidance documents - Institute for Health and Consumer ...

technical guidance documents - Institute for Health and Consumer ...

technical guidance documents - Institute for Health and Consumer ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Guidance <strong>for</strong> calculating PEClocal in soil<br />

is given <strong>for</strong> the following exposure<br />

routes:<br />

• application of sewage sludge in<br />

agriculture;<br />

• dry <strong>and</strong> wet deposition from the<br />

atmosphere.<br />

Direct application of substances (on the<br />

basis of the maximum recommended<br />

application rate; e.g. pesticide adjuvants<br />

or fertilisers) is not taken into account.<br />

Guidance may need to be developed in<br />

the future.<br />

ENVIRONMENTAL EXPOSURE ASSESSMENT<br />

For sludge application to agricultural soil an application rate of 5,000 kg/ha dry weight per year is<br />

assumed while <strong>for</strong> grassl<strong>and</strong> a rate of 1000 kg/ha/yr should be used. Sludge application is treated as<br />

a single event once a year. The contribution to the overall impact from wet <strong>and</strong> dry deposition is<br />

based on the emission calculation of a point source (Section 2.3.8.2) <strong>and</strong> is related to a surrounding<br />

area within 1000 m from that source. The deposition is averaged over the whole area.<br />

Atmospheric deposition is assumed to be a continuous flux throughout the year. It should be<br />

noted that the deposition flux is averaged over a year. This is obviously not fully realistic, since<br />

the deposition flux is linked to the emission episode. Averaging is done to facilitate calculation<br />

of a steady-state level. Furthermore, it is impossible to indicate when the emission episode takes<br />

place within a year: in the beginning of the growing season, any impact on exposure levels will<br />

be large, after the growing season, the impact may well be insignificant. There<strong>for</strong>e, averaging<br />

represents an appropriate scenario choice.<br />

The PEC in agricultural soil is used <strong>for</strong> two purposes:<br />

• <strong>for</strong> risk characterisation of terrestrial ecosystems (Section 4);<br />

• as a starting point <strong>for</strong> the calculation of indirect human exposure via crops <strong>and</strong> cattle<br />

products (see Chapter 2: Risk Assessment <strong>for</strong> Human <strong>Health</strong>).<br />

There are several extensive numerical soil <strong>and</strong> groundwater models available (mainly <strong>for</strong><br />

pesticides). These models, however, require a detailed definition of soil <strong>and</strong> environmental<br />

characteristics. This makes this type of models less appropriate <strong>for</strong> a generic risk assessment at<br />

EU-level. For the initial assessment, a simplified model is used. The top layer of the soil<br />

compartment is described as one compartment, with an average influx through aerial deposition<br />

<strong>and</strong> sludge application, <strong>and</strong> a removal from the box by degradation, volatilisation, leaching, <strong>and</strong><br />

other processes if relevant. The concentration in this soil box can now be described with a simple<br />

differential equation.<br />

The initial concentration, Csoil(0), is governed by the input of the substance through sludge<br />

application.<br />

dC<br />

dt<br />

soil<br />

volatilization<br />

degradation<br />

= - k • C soil + Dair<br />

(51)<br />

air<br />

soil water<br />

leaching<br />

solids<br />

Figure 10 Fate processes in the soil compartment.<br />

partitioning<br />

79

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!