The use of two amendments (peat and lime) to reduce metal mobility, salinity and toxicity in harbour bottom sediments

The aim of the study was to assess the effectiveness of using peat (P) and lime (L) to immobilise metals and reduce salinity in contaminated harbour sediments (BS), in order to aid remediation. The contaminated BS1 and the uncontaminated BS2 were mixed with P and L in the following proportions: 60% BS and 40% P; 60% BS, 20% P and 20% L; 60% BS and 40% L. Greater effectiveness was found for lime than for peat. In mixtures with lime, the proportion of metals in the residual fraction increased more frequently. Both additives were effective in reducing the mobile fraction (F1) of metals. Only the addition of peat increased the F1 Cd due to a significant decrease in pH in the peat-containing mixtures. Salinity decreased significantly (by 14-61%) when additives were applied. Adding lime and peat to the sediments altered the composition of the functional groups and structures, which could be potentially responsible for interactions with metals. In particular, the addition of peat increased the pool of o-carboxyl groups, whereas the incorporation of lime, peat, or their mixture elevated the population of moderately and weakly acidic functional groups, including simple carboxylic and phenolic moieties. In lime-derived treatments, an increase in carbonate content was also observed. Peat reduced the fractal dimension of the surface, indicating a simplification of the structure and a reduction in surface roughness. Lime increased the hydrophilicity of BS, potentially influencing interactions between dissolved metal species and internal sorption sites. The most sensitive organisms were the plants (BS1, BS2), and Alivibrio fischeri (except BS2 + P + L).