A review and critical assessment of sedimentary metal indices used in determining the magnitude of anthropogenic change in coastal environments

• Published in: The Science of the total environment 2023-01, Vol.854, p.158129, Article 158129
• Main Author: Birch, G.F.
• Format: Article
• Language: English
• Subjects: Background; Coastal; Contamination; Enrichment; Normalisation; Pollution; Reference value
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.158129

The current critical review examines the application of 11 frequently used sedimentary metal indices in their ability to accurately assess the magnitude of human-induced change (enrichment) in the highly vulnerable and intensely developed coastal environment. The plethora and rapidly increasing number of sedimentary metal indices should, if not derived for special purposes, produce a consistent assessment on the basis that they use the same suite of metals and concentrations. Inconsistent numerical results produced by different index formulations should, when combined with their associated classification scheme, produce a common assessment of environmental condition. However, such a consistent outcome is seldom observed. Significant differences in assessment results are partly due to the historical evolution of indices and to the extraordinary diversity of background and reference values and materials being applied to account for pre-anthropogenic metal levels and confounding due to variable sediment characteristics. Size-normalised sample and background metal data used in the mCd and MEQ indices do not require reference values to account for textural variability and provide a quasi-direct measurement of enrichment with minimal computation (simple division). These priority indices should be combined into a single index (Enrichment Quotient, EQ). Results produced by the EF index were strongly correlated to mCd and MEQ and provide a similar classification and is recommended if normalised data are unavailable. Other indices assessed (MPI, PI, mPI, SEF, Igeo, PLI and Cf, original and current) provided a range of results, which either over- or under-estimated enrichment. The confusion concerning the choice and application of background and reference values in the assessment process is reviewed and their use in local and global assessment is clarified. Single- and combined-metal evaluations are recommended to provide detailed, local and more comprehensive assessments, respectively. [Display omitted] •First critical evaluation of frequently used sedimentary metal indices•Examination of inconsistent results produced by different index formulations•mCd and MEQ indices provided best measurement of enrichment•Enrichment Factor recommended for total sediment chemical data•Classification schemes failed to modify inconsistent evaluations