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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