Story Name: Mercury Contamination in Bass

Abstract: Mercury contamination of edible freshwater fish poses a direct threat
to our health. Largemouth bass were studied in 53 different Florida lakes to
examine the factors that influence the level of mercury contamination. Water
samples were collected from the surface of the middle of each lake in August 1990
and then again in March 1991. The pH level, the amount of chlorophyll, calcium,
and alkalinity were measured in each sample. The average of the August and March
values were used in the analysis. Next, a sample of fish was taken from each lake
with sample sizes ranging from 4 to 44 fish. The age of each fish and mercury
concentration in the muscle tissue was measured. (Note: Since fish absorb mercury
over time, older fish will tend to have higher concentrations).

Thus, to make a fair comparison of the fish in different lakes, the investigators
used a regression estimate of the expected mercury concentration in a three year
old fish as the standardized value for each lake. Finally, in 10 of the 53 lakes,
the age of the individual fish could not be determined and the average mercury
concentration ofthe sampled fish was used instead of the standardized value.

Florida has set a standard of 1/2 part per million as the unsafe level of mercury
concentration in edible foods. 45.3% of the lakes exceed this level.

The smallest level of mercury concentration that the measuring instrument can
detect is 40 parts per billion. Any level below that was set to 40 parts per
billion. This, of course, "flatens out" the slope of the relationship at the low
end as well as affecting the standardized values. These observations are usually
on young fish.

Logarithmic transformations on some of the variables provide insight into the
relationships among the other variables in the study. Alkalinity level may be
associated with mercury concentration, and may help account for the higher levels
of mercury.

Reference: Lange, Royals, & Connor. (1993). Transactions of the American
Fisheries Society . Authorization: contact authors Description: Largemouth bass
were studied in 53 different Florida lakes to examine the factors that influence
the level of mercury contamination. Water samples were collected from the surface
of the middle of each lake in August 1990 and then again in March 1991. The pH
level, the amount of chlorophyll, calcium, and alkalinity were measured in each
sample. The average of the August and March values were used in the analysis.
Next, a sample of fish was taken from each lake with sample sizes ranging from 4
to 44 fish. The age of each fish and mercury concentration in the muscle tissue
was measured. (Note: Since fish absorb mercury over time, older fish will tend to
have higher concentrations). Thus, to make a fair comparison of the fish in
different lakes, the investigators used a regression estimate of the expected
mercury concentration in a three year old fish as the standardized value for each
lake. Finally, in 10 of the 53 lakes, the age of the individual fish could not be
determined and the average mercury concentration ofthe sampled fish was used
instead of the standardized value. Number of cases: 53 Variable Names:

1.ID: ID number
2.Lake: Name of the lake
3.Alkalinity: Alkalinity (mg/L as Calcium Carbonate)
4.pH: pH
5.Calcium: Calcium (mg/l)
6.Chlorophyll: Chlorophyll (mg/l)
7.Avg_Mercury: Average mercury concentration (parts per million) in the muscle tissue of the fish sampled from that lake
8.No.samples: How many fish were sampled from the lake
9.min: Minimum mercury concentration amongst the sampled fish
10.max: Maximum mercury concentration amongst the sampled fish
11.3_yr_Standard_mercury : Regression estimate of the mercury concentration in a 3 year old fish from the lake (or = Avg Mercury when age data
was not available)
12.age_data: Indicator of the availability of age data on fish sampled

The Data:

ID Lake Alkalinity pH Calcium Chlorophyll Avg_Mercury No.samples min max 3_yr_Standard_Mercury age_data
1 Alligator 5.9 6.1 3.0 0.7 1.23 5 0.85 1.43 1.53 1
2 Annie 3.5 5.1 1.9 3.2 1.33 7 0.92 1.90 1.33 0
3 Apopka 116.0 9.1 44.1 128.3 0.04 6 0.04 0.06 0.04 0
4 Blue Cypress 39.4 6.9 16.4 3.5 0.44 12 0.13 0.84 0.44 0
5 Brick 2.5 4.6 2.9 1.8 1.20 12 0.69 1.50 1.33 1
6 Bryant 19.6 7.3 4.5 44.1 0.27 14 0.04 0.48 0.25 1
7 Cherry 5.2 5.4 2.8 3.4 0.48 10 0.30 0.72 0.45 1
8 Crescent 71.4 8.1 55.2 33.7 0.19 12 0.08 0.38 0.16 1
9 Deer Point 26.4 5.8 9.2 1.6 0.83 24 0.26 1.40 0.72 1
10 Dias 4.8 6.4 4.6 22.5 0.81 12 0.41 1.47 0.81 1
11 Dorr 6.6 5.4 2.7 14.9 0.71 12 0.52 0.86 0.71 1
12 Down 16.5 7.2 13.8 4.0 0.50 12 0.10 0.73 0.51 1
13 Eaton 25.4 7.2 25.2 11.6 0.49 7 0.26 1.01 0.54 1
14 East Tohopekaliga 7.1 5.8 5.2 5.8 1.16 43 0.50 2.03 1.00 1
15 Farm-13 128.0 7.6 86.5 71.1 0.05 11 0.04 0.11 0.05 0
16 George 83.7 8.2 66.5 78.6 0.15 10 0.12 0.18 0.15 1
17 Griffin 108.5 8.7 35.6 80.1 0.19 40 0.07 0.43 0.19 1
18 Harney 61.3 7.8 57.4 13.9 0.77 6 0.32 1.50 0.49 1
19 Hart 6.4 5.8 4.0 4.6 1.08 10 0.64 1.33 1.02 1
20 Hatchineha 31.0 6.7 15.0 17.0 0.98 6 0.67 1.44 0.70 1
21 Iamonia 7.5 4.4 2.0 9.6 0.63 12 0.33 0.93 0.45 1
22 Istokpoga 17.3 6.7 10.7 9.5 0.56 12 0.37 0.94 0.59 1
23 Jackson 12.6 6.1 3.7 21.0 0.41 12 0.25 0.61 0.41 0
24 Josephine 7.0 6.9 6.3 32.1 0.73 12 0.33 2.04 0.81 1
25 Kingsley 10.5 5.5 6.3 1.6 0.34 10 0.25 0.62 0.42 1
26 Kissimmee 30.0 6.9 13.9 21.5 0.59 36 0.23 1.12 0.53 1
27 Lochloosa 55.4 7.3 15.9 24.7 0.34 10 0.17 0.52 0.31 1
28 Louisa 3.9 4.5 3.3 7.0 0.84 8 0.59 1.38 0.87 1
29 Miccasukee 5.5 4.8 1.7 14.8 0.50 11 0.31 0.84 0.50 0
30 Minneola 6.3 5.8 3.3 0.7 0.34 10 0.19 0.69 0.47 1
31 Monroe 67.0 7.8 58.6 43.8 0.28 10 0.16 0.59 0.25 1
32 Newmans 28.8 7.4 10.2 32.7 0.34 10 0.16 0.65 0.41 1
33 Ocean Pond 5.8 3.6 1.6 3.2 0.87 12 0.31 1.90 0.87 0
34 Ocheese Pond 4.5 4.4 1.1 3.2 0.56 13 0.25 1.02 0.56 0
35 Okeechobee 119.1 7.9 38.4 16.1 0.17 12 0.07 0.30 0.16 1
36 Orange 25.4 7.1 8.8 45.2 0.18 13 0.09 0.29 0.16 1
37 Panasoffkee 106.5 6.8 90.7 16.5 0.19 13 0.05 0.37 0.23 1
38 Parker 53.0 8.4 45.6 152.4 0.04 4 0.04 0.06 0.04 0
39 Placid 8.5 7.0 2.5 12.8 0.49 12 0.31 0.63 0.56 1
40 Puzzle 87.6 7.5 85.5 20.1 1.10 10 0.79 1.41 0.89 1
41 Rodman 114.0 7.0 72.6 6.4 0.16 14 0.04 0.26 0.18 1
42 Rousseau 97.5 6.8 45.5 6.2 0.10 12 0.05 0.26 0.19 1
43 Sampson 11.8 5.9 24.2 1.6 0.48 10 0.27 1.05 0.44 1
44 Shipp 66.5 8.3 26.0 68.2 0.21 12 0.05 0.48 0.16 1
45 Talquin 16.0 6.7 41.2 24.1 0.86 12 0.36 1.40 0.67 1
46 Tarpon 5.0 6.2 23.6 9.6 0.52 12 0.31 0.95 0.55 1
51 Tohopekaliga 25.6 6.2 12.6 27.7 0.65 44 0.30 1.10 0.58 1
47 Trafford 81.5 8.9 20.5 9.6 0.27 6 0.04 0.40 0.27 0
48 Trout 1.2 4.3 2.1 6.4 0.94 10 0.59 1.24 0.98 1
49 Tsala Apopka 34.0 7.0 13.1 4.6 0.40 12 0.08 0.90 0.31 1
50 Weir 15.5 6.9 5.2 16.5 0.43 11 0.23 0.69 0.43 1
52 Wildcat 17.3 5.2 3.0 2.6 0.25 12 0.15 0.40 0.28 1
53 Yale 71.8 7.9 20.5 8.8 0.27 12 0.15 0.51 0.25 1