Dredged sediments as a plant-growing substrate: Estimation of health risk index

Dredging of sediments is conducted worldwide to maintain harbours and water bodies. As a result, large amounts of materials generated require proper management and could have useful applications in a circular economy context. The current use of peat as organic material in cultivating plants requires urgent replacement by more sustainable alternatives. In this context, using nutrient-rich sediments generated by dredging could be an attractive option. However, due to contaminants in dredged sediments, more investigations are required. The present study investigated the potential to employ dredged material as a plant-growing substrate to cultivate lettuce (Lactuca sativa). The study employed compost and dredged sediments from Malmfjärden Bay, Sweden, with low and high nutritional content (LN and HN, respectively), with and without polymer (PO) used for dewatering. The tests were carried out under controlled conditions in a greenhouse, and the studied substrates were (% vol): (1) 100 % sediment (100S^HN); (2) 50 % sediment +50 % compost (50S^LN-50C); (3) 70 % sediment +30 % compost (70S^LN-30C); (4) 50 % polymer sediment +50 % compost (50S^PO-50C); and (5) 100 % compost (100C). Fertilisers were added to 50S^LN-50C and 70S^LN-30C during the experiment. Lettuces with the highest weight were harvested from substrates 100C, 50S^PO-50C and 50S^LN-50C. However, the lettuces only reached a weight of 18.57 ± 4.67 g. The results showed that a main limitation of the growth was probably a lack of aeration of the sediments during sampling and development of the experiment. The low aeration possibly caused a lack of available forms of N in the substrates, hindering the growth. Lettuces harvested from substrates containing sediments presented Cd concentrations slightly overpassing the Swedish thresholds, and the health risk index was marginally exceeding 1. Hence, sediments need to be pre-treated before using them to cultivate edible crops, or they could be employed to cultivate ornamental or bioenergy plants.