マガキ個体群における重金属含量の頻度分布型と高濃度縮個体の存在

抄録

Copper, Zn, Fe, Mn and Cd contents in whole soft bodies of 340 specimens of a Pacific oyster Crassosrrea gigas were determined individually to make clear their statistical characteristics, such as frequency distribution patterns, their relating statistics, correlations and regressions among biological parameters and heavy metal contents, high-concentrators in the range of high dispersion and their definition, etc.
The histograms for the five metals were asymmetrical patterns with positive skewness, and those of Fe and Mn indicated much higher dispersion than those of Cu, Zn and Cd. The histogram for Mn fitted most adequately to logarithmic normal distribution compared to those of the other four metals.
Simple arithmetic and geometric means (SAM and SGM), modes (Mo) and medians (Me) were arranged as follows: SAM>Me>SGM>Mo for Cu, Mn and Cd; SAM>Me>Mo>SGM for Zn; and SAM>SGM>Me>Mo for Fe.
The extremes of the contents ranged from 96.2 to 1270 for Cu, 78.1 to 1070 for Zn, 15.8 to 732 for Fe containing the two extremely high values, 0.56 to 16.6 for Mn, and 0.056 to 0.799 for Cd (ppm on a fresh wt basis). The ratios (max./mint.) were as follows: Fe (46.27)>Mn (24.64)>Cd (14.27)>Zn (13.70)>Cu (13.20).
The individuals with the high metal contents beyond μ+3σ of the first normal distribution separated on normal probability diagrams were termed as the high-concentrators and their ap-pearance numbers and rates were 2 and 0.59% for Cu, 3 and 0.88% for Zn, 12 and 3.53% for Fe, 17 and 5.00% for Mn and 3 individuals and 0.88% for Cd. These high-concentrators appeared independently irrespective of heavy metal species except the combination of Cu/Zn.