Table 3 - Percent of Great Lakes Loadings Attributable to the Atmospheric Deposition Pathway1

Pollutant

Lake Superior

Lake Michigan

Lake Huron

Lake Erie

Lake Ontario

B(a)P

96

86

80

79

72

PCDD/F

80-100

50-100 (PCDD);

5-35 (PCDF)

86

~40

5-35 (PCDD);

< 5 (PCDF);

HCB

99

95

96

> 17

40

Lead

64-97

99

98

46

73

Mercury2

73

> 80

-

-

-

PCBs

82-95

58

78

13

7

DDT

97

98

97

22

31

Atrazine

97

23-30

~20

~10-20

~5

Mirex

-

-

-

-

~5

1

There are significant uncertainties in most, if not all, of the estimates in this table.

2

Lake Michigan cites Mason & Sullivan (M&S). M&S define “atmospheric deposition” as an estimate of mercury that deposits directly onto the lake, but does not account for atmospheric deposition to tributaries, which would then enter the lake. This direct deposition accounts for 82 percent of estimated loadings and an estimated 27 percent is attributed to “riverine input” without any attribution of how the mercury got into the river in the first place. It is likely that most of it came from atmospheric sources, with smaller amounts coming from direct water discharges and contaminated sediment. This is likely also the case for the Lake Superior estimate.

Source: 1997-99 Priorities and Progress Under the Great Lakes Water Quality Agreement, Report to the International Joint Commission, January 2000 p. 114.