3.3.9           Weighting category Degradability

Substances brought into nature, there, by photolysis, hydrolysis, or metabolic activity of organisms, are degraded to inorganic materials, which again enter the materials’ metabolism, e.g., the carbon or nitrogen cycle. The nature’s intake capacity for substances of, especially anthropogenic origin, and the ability to degrade them, is restricted. Substances that accumulate in nature and are degraded poorly are called ‘persistent’. For example, we indicate the plant protective agents Aldrin, Chlordan, and the industry-chemical hexachlorobenzene, which production even was forbidden, recently, counted among the persistent semi-volatile substances (POPs, Persistent Organic Pollutants). A measurement for the degradability is the half-life period. Substances are classified as to be degradable quickly if the half-life period (HLP) comes up to one week and as resistant if it comes up to one year. Therefore, in EATOS the period of one week the weighting factor Q = 2 was assigned to, and the period of one year the value 10. A linear split of the value ranges for Q is shown in Table 12.

 

Table 12  Assignment of half-life periods to the weighting factor QDegradability

Q

 

half-life [h]

 

 

 

 

 

1

0

to

168

»

7

days

fast (1 - 7 days)

2

168

to

1242

»

52

days

moderate (1 - 4 weeks)

3

1242

to

2316

»

97

days

 

4

2316

to

3390

»

141

days

 

5

3390

to

4464

»

186

days

slow (1 - 6 months)

6

4464

to

5538

»

231

days

 

7

5538

to

6612

»

276

days

 

8

6612

to

7686

»

320

days

 

9

7686

to

8760

»

365

days

resistant (6 - 12 months)

10

8760

to

<

 

 

 

 

                       

From the coordinates (Q = 2 / HLP = 186 h) and (Q = 10 /HLP = 8760 h) the function HLP = 1074 × Q - 1980 results, wherefrom - at HLP given - the weighting factor  Q = [(HLP + 1980) / 1074] arises.

The degradation of chemicals takes place in different compartments. The kind of reduction can be indicated in EATOS to be able to assign the data-affiliation, but no diversely distinguished assignment of the weighting factor Q is made.

 

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