Characterization of how contaminants arise in a dredged marine sediment and analysis of the effect of natural weathering

Abstract

Millions of tons of contaminated sediments are dredged each year from the main harbors in France. When removed from water, these sediments are very reactive, therefore their geochemical behavior must be understood in order to avoid dispersion of contaminated lixiviates in the surrounding soils. In this objective, it is necessary to evaluate the principal physicochemical parameters, and also achieve advanced mineralogical characterization. These studied sediments are highly contaminated by metals, notably copper (1445 and 835mg/kg, in the unweathered and naturally-weathered sediments, respectively), lead (760 and 1260mg/kg, respectively), zinc (2085 and 2550mg/kg, respectively), as well as by organic contaminants (PAH, PCB) and organometallics (organotins). A high concentration of sulfide minerals was also observed both in the unweathered sediment preserved under water (3.4wt% of pyrite especially), and in the naturally weathered sediment (2wt% pyrite), and in particular framboïdal pyrite was observed in the two materials. The presence of reactive mineral species in the naturally-weathered sediment can be explained by the deposit of a protective layer, composed of sulfide and their oxidation products (sulfate and iron oxides), thus preventing oxygen from diffusing through to the sulfide minerals. Additionally, the presence of aluminosilicates aggregates coating the sulfide minerals could also explain their presence in the naturally-weathered sediment. As organic matter is one of the principal constituents of the sediments (5.8 and 6.3wt% total organic carbon in the unweathered and weathered sediment, respectively), the aggregates are probably partially constituted of refractory humic material. It therefore appears that the natural weathering has led to a significant decrease in PAHs and organotins, but not in PCBs. The evolution of the granulometric structure and the distribution of the metallic contaminants could therefore lead us to consider a treatment by size separation, and a possible valorization of the dredged sediments in civil engineering.

A consideration of polychlorinated biphenyls as a chemostratigraphic marker of the Anthropocene

“…By contrast, studies on marine sediment cores collected from the Palos Verdes Shelf (California, USA), where municipal wastes had been deposited for about 45 years, showed no indication of PCB transformation by diagenetic processes (Eganhouse et al, 2000). Furthermore, in a study on weathering of marine sediments stored for 5 years in an outdoor environment after dredging, Couvidat et al (2018) showed that concentrations of PCBs remained constant, whereas the concentrations of other organic pollutants, such as polycyclic aromatic hydrocarbons and organotin compounds substantially decreased. Hence under favorable sedimentary conditions, environmental records of PCBs may remain stable for many decades and possibly centuries.…”

“…Furthermore, in a study on weathering of marine sediments stored for 5 years in an outdoor environment after dredging, Couvidat et al (2018) showed that concentrations of PCBs remained constant whereas the concentrations of other organic pollutants, such as polycyclic aromatic hydrocarbons and organotin compounds substantially decreased. Hence under favorable sedimentary conditions, environmental records of PCBs may remain stable for many decades and possibly centuries.…”

Stabilization/solidification of sediments: challenges and novelties

“…For this these reasons, contaminated sediments need to be properly managed to eliminate risk of contamination. Sediments dredging before their stabilization and/or revalorization is widely used for contaminated sediments management [3][4][5][6][7]. However, sediments dredging changes their environmental conditions in terms of temperature, humidity, redox potential, grain accessibility by oxidizing agents (e.g.…”

Behavior of Cementitious Materials under the Effect of an Eco-Cement Based on Dredged Sludge

“…By contrast, the calcination of the sludge only generates water vapor [12]. As a result, some researchers have partially replaced Portland cement in concrete with calcinated sludge [13,14]. In the cement industry, the recent research of sludge vaporization mainly characterizes physical, chemical, mineralogical, and sustainability features.…”