Abstract:
The article presents the index MeTo which is elaborated to assess the hazard of heavy metal pollution of riverine floodplain soils in the Danube lowlands in Bulgaria. The index MeTo includes the following parameters: degree of heavy metal pollution of river sediment (Ме) and topography (To). Each parameter is characterized by the following elements: weight (W), ranges, and ratings (R). The two variables are weighed against each other to determine its relative importance. The higher weight is given to the indicator ‘degree of heavy metal pollution of river sediment’ followed by the ‘topography’. Their weight coefficients are 2 and 1, respectively. The ranges of the parameters characterize the variety of environmental settings throughout the wetlands for the accumulation of heavy metals in the soils of the floodplain. Ratings (R) from 1 to 4 is assigned to each of the ranges of the individual variables. The degree of pollution of the river sediment is calculated by the index Cd proposed by Backman et al. (1998) as follows: , , where Cfi is for the contamination factor for the i–th component, Cai is for the analytical value of the i–th component, and Cni is for the threshold value of the i–th component. The target values for sediment used in the consecutive Joint Danube Surveys organized by the International Commission for the Protection of the Danube River are applied as contaminant thresholds for calculating the index Cd. The ranges of Cd are determined as follows: Cd=0, no pollution; Cd (0, 1], low pollution; Cd (1, 3], moderate pollution; Cd>3, high pollution. The intervals have scores 1, 2, 3, and 4, respectively. The topography is assessed by the major geomorphological forms identified in the lowlands, which are rated as follows: high floodplain, R=1; sandy ridges, R=1; low floodplain, R=2; old river channels, R=3; marshes, R=4. The MeTo index is calculated as the sum of the products of ratings (R) and weights (W) assigned to each of the parameters: MeTo=МеW*MeR+ToW*ToR. The minimum value of the MeTo index is 3 and the maximum is 12. The whole range is divided into six classes: 3 (negligible hazard), 4-5 (very low hazard), 6-7 (low hazard), 8-9 (moderate hazard), 10-11 (high hazard), and 12 (very high hazard).