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Calculation of PEClocalsoil<br />

For soil, three different PECs are calculated, <strong>for</strong> different endpoints (Table 11).<br />

Table 11 Characteristics of soil <strong>and</strong> soil-use <strong>for</strong> the three different endpoints<br />

Depth of soil<br />

compartment<br />

Averaging time Rate of sludge application Endpoint<br />

[m] [days] [kgdwt . m -2. year -1 ]<br />

ENVIRONMENTAL EXPOSURE ASSESSMENT<br />

PEClocalsoil 0.20 30 0.5 terrestrial ecosystem<br />

PEClocalagr. soil 0.20 180 0.5 crops <strong>for</strong> human consumption<br />

PEClocalgrassl<strong>and</strong> 0.10 180 0.1 grass <strong>for</strong> cattle<br />

The “depth of soil” represents the depth range <strong>for</strong> the top soil layer which is of interest. The<br />

depth of 20 cm is taken because this range usually has a high root density of crops, <strong>and</strong><br />

represents the ploughing depth. For grassl<strong>and</strong>, the depth is less since grassl<strong>and</strong>s are not<br />

ploughed. The averaging period of 180 days <strong>for</strong> crops is chosen as a representative growing<br />

period <strong>for</strong> crops. For grassl<strong>and</strong> this period represents a reasonable assumption <strong>for</strong> the period that<br />

cattle is grazing on the field. For the ecosystem a period of 30 days is taken as a relevant time<br />

period with respect to chronic exposure of soil organisms.<br />

The concentration at the regional scale is used as background concentration <strong>for</strong> the local scale.<br />

For this purpose, the concentration in unpolluted soil needs to be applied (“natural soil”, only<br />

input through deposition). Otherwise, sludge application is taken into account twice.<br />

Explanation of symbols<br />

PEClocal soil = Clocal soil + PECregional natural soil<br />

(66)<br />

Clocalsoil local concentration in soil [mg . kg -1 ] eq. (54)<br />

PECregionalnatural soil regional concentration in natural soil [mg . kg -1 ] 2.3.8.7<br />

PEClocalsoil predicted environmental conc. in soil [mg . kg -1 ]<br />

The equation <strong>for</strong> deriving the concentration in the pore water is:<br />

Explanation of symbols<br />

PEClocal soil, porew =<br />

PEClocal RHO<br />

K soil-water • 1000<br />

soil • soil<br />

PEClocalsoil predicted environmental conc. in soil [mg . kg -1 ] eq. (66)<br />

Ksoil-water soil-water partitioning coefficient [m 3. m -3 ] eq. (24)<br />

RHOsoil bulk density of wet soil [kg . m -3 ] eq. (18)<br />

PEClocalsoil,porew predicted environmental conc. in porewater [mg . l -1 ]<br />

(67)<br />

85

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