|
Analysis:
Table W1-20. Plausibility of different effects
| Specific Effect |
Mechanism |
References |
| Increased relative weight |
No known mechanism |
|
| Increased DELT |
Metals cause fin erosion and lesions. PB, Zn, and Cu cause deformities |
1,2,3 |
| Decreased percent mayflies |
Metals cause lethal and sublethal effects on invertebrates |
4,5 |
Discussion:
Decreased percent mayflies and increased DELT can be
linked to metals contamination. No plausible mechanism is known
by which increased metals leads to increased relative weight.
Evidence Scoring Table:
| Finding |
Interpretation |
Score |
| A plausible mechanism exists. |
This finding somewhat supports the case for the candidate cause, but is not strongly supportive because levels of the agent may not be sufficient to cause the observed effect. |
+ |
| No mechanism is known. |
This finding neither supports nor weakens the cause for the candidate cause. |
0 |
| The candidate cause is mechanistically implausible. |
This finding strongly weakens the case for the candidate cause, but is not convincing because the mechanism could be unknown. |
-- |
Table W1-21. Mechanistically plausible cause scores for candidate causes.
| Candidate Cause |
Specific Effects |
Result |
Score |
| Metals |
Increased relative weight |
Implausible: no known mechanisms |
-- |
| Increased DELT |
Plausible |
+ |
| Decreased percent mayflies |
Plausible |
+ |
|