Normalization procedures for sediment contaminants in spatial and temporal trend monitoring

Abstract

Rational pollution, or the effectiveness of natural attenuation assessments based upon estimating the degree of contamination, critically depends on the basis of a sound normalization to take into account heterogeneous sedimentary environments. By normalizing the measured contaminant concentration patterns for the sediment characteristics, the inherent variability can be reduced and so allow a more meaningful assessment of both the spatial distributions and the temporal trends. A brief overview and guidance in the methodology available for choosing an appropriate site-specific normalization approach is presented. This is followed by general recommendations with respect to the choice of normalizer and the necessary geochemical and statistical quality assurance methods, with support from the results of recent international intercomparison exercises within the QUASH (Quality Assurance of Sample Handling) programme, as well as discussions within the International Commission on the Exploration of the Sea (ICES) working groups. The most important of these recommendations is the use of a two-tiered normalization approach including wet sieving (<63 microm), followed by an additional geochemical co-factor normalization.

Concentration and fractionation of trace metals in surface sediments of intertidal Bohai Bay, China

“…A range of geochemical data normalization methods can be used to compensate for the influence of the natural variability in sediment mineralogical composition, and identify anomalous metal concentrations (e.g. Loring and Rantala, 1992;Kersten and Smedes, 2002).…”

Evaluacion de la calidad ambiental de los sedimentos marinos en el sistema de bahias de Caldera (27 S), Chile

“…Si bien el análisis de metales en una fracción determinada no refleja el contenido total en los sedimentos (Liaghati et al, 2003), este procedimiento permite corregir la variabilidad natural del tamaño de partículas constituyentes de los sedimentos marinos y comparar diferentes ambientes de depositación (Padmalal et al, 1997;Kersten & Smedes, 2002).…”

Grain size normalization: a case for post extraction normalization and inclusion of selective extraction procedures

“…They include wet sieving followed by chemical analysis of only the fine fraction or alternatively analysis of a bulk homogenous sample in combination with wet sieving of a separate subsample and then mathematically expressing the fine fraction concentrations as 100% of the total sample weight. In recent times, mechanical sieving is often conducted in conjunction with a Type 4 (Table 1) normalization to enhance analytical detection (Kersten and Smedes 2002). Nevertheless, where sediments contain appreciable quantities of fine-grained aggregates or coatings, any mechanical sieving will almost certainly result in a loss of both bioavailable and total analytes as part of the coarse fraction.…”

“…problem is most acute where the sediment is anoxic and reduced, even when sediments are size separated and handled in an anaerobic chamber (e.g., Thomson et al 1980;Kersten and Förstner 1986;Rapin et al 1986;Ajayi and Vanloon 1989;Förstner 1989). …”

“…Despite the vast array of normalization techniques (Table 1), sediments are commonly size normalized, or size normalized in combination with a chemical extraction (Kersten and Smedes 2002; i.e., Type 4 - Table 1). Size normalization is almost invariably completed before chemical analysis by wet sieving with ambient, or high-purity laboratory water.…”