Table 2.

Summary of evidence for mine-derived lead toxicity as the cause of mass mortality of tundra swans in the Coeur d’Alene River watershed. Based on evidence from (URS Greiner Inc and CH2M Hill 2011). The weight of evidence for the properties of each implication of the evidence is indicated by + for supporting, ‒ for weakening, and 0 for uninformative information.

Causal Characteristic	Evidence	Relevance/Reliabilitya
Antecedents	• Spills of Pb mine tailings and atmospheric deposition from smelters account for the high sediment Pb levels.	+++/++
	• Hunting occurs elsewhere on flyway, not known locally	+/++
Time order	• No evidence—no pre-mining information on swan mortality	0/0
Co-occurrence	• Swan kills occurred in Pb-contaminated lakes and wetlands and not elsewhere in the region.	+++/++
Sufficiency	• Mortality occurred in laboratory tests of other avian species at Pb doses lower than those estimated for swans in the field.	++/++
	• Mortality occurred in laboratory tests of other avian species at Pb body burdens observed in dead or moribund swans in the field.	++/++
	• Severe sublethal effects occurred in swans fed a diet with 24% contaminated sediment.	++/+++
	• Consistent mortality was observed in the field at blood Pb levels >0.5 μg/g.	+++/++
Interaction	• Pb-contaminated sediments were found in swan guts and excreta.	+++/+++
	• Dead and moribund swans had high blood and liver Pb levels.	++/++
	• Lead shot was NOT found in Swan crops.	− − −
Mechanism	• Pb-contaminated Coeur d’Alene sediments fed to swans caused numerous adverse effects that caused emaciation and weakened the swans.	+++/+++
Specific alteration	• Swans in the field and the sediment feeding study had pathologies characteristic of Pb toxicity, particularly, enlarged gall bladders containing viscous dark green bile.	+++/+++
Collective Properties	Body of Evidence	Properties: Reliability
Number	• Most types of evidence have only one study.	0
Diversity	• There are several types of field and laboratory studies.	+++
Coherence	• All results support the causal hypothesis and are logically concordant.	+++
Absence of bias	• Critical evidence is from federal contractors or agencies who are unlikely to have conflicts of interest.	0
	• Data quality was rigorously assured and documented.	+++
Integrated WoE
Finding	Exceptionally consistent, relevant and reliable body of evidence implicates mining derived Pb as the cause of swan kills in the Coeur d’Alene River watershed.	+++
	Pb toxicity from Pb shot refuted by lack of exposure.	− − −

^a+++ convincingly supports, ++ strongly supports, + somewhat supports, 0 neutral or ambiguous