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

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 devel-oped 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 nu-merical 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 ob-served. Significant differences in assessment results are partly due to the historical evolution of indices and to the extraor-dinary 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.

Automated summary

This critical review examines the application of 11 sedimentary metal indices in assessing human-induced change in coastal environments. The study finds that the use of different indices leads to inconsistent assessment results, partly due to the historical evolution of indices and the diversity of background and reference values. The study recommends combining priority indices into a single index and using single and combined metal evaluations for detailed and comprehensive assessments.