Martinique’s DEAL (environment directorate) manages the maintenance of rivers and is responsible for dredging and onshore sediment management where necessary. However, the presence of copper and the contamination of some soils by chlordecone raises the question of the dangerousness of sediments in some rivers and what becomes of them after dredging.
13 December 2019
A mechanical shovel taking sediment samples from the Salt River

A mechanical shovel taking sediment samples from the Salt River (Martinique).

© BRGM - Philippe Bataillard

The need  

Waste is classified as hazardous after information on 15 properties is taken into account. A waste will thus be considered hazardous if it fails any one of the fifteen tests listed in Regulation 1357/2014/EU. This methodology has been deployed in Martinique by DEAL and BRGM to assess the hazardous nature (or not) of the sediments of the Salt River. 

The results  

The properties HP1, HP2, HP3 and HP15 are not relevant for dredged sediments, and were not determined. The hazard characterization of the samples showed that  the materials were not hazardous regarding the properties HP4 to HP8, HP10, HP11, HP13 and HP14. Though it could be demonstrated that it was not relevant to measure the property HP12, it was still necessary to investigate the property HP9, relating to the "infectious” danger and for which there is no available measurement or reference protocol. To this end, a parallel was drawn between the onshore management of dredged sediments and the spreading of sewage sludge as well as with the NF U44-551 standard, relating to cultivation substrates (AFNOR, 2009). 

Sediments showed systematic excessive values of the order of 1.5 to 2 times the 100 mg/kg S1 threshold value for copper. Chlordecone, two of chlordecone’s metabolites, AMPA (aminomethylphosphonic acid), glyphosate, anthracene, benzo[ghi]perylene, pyrene and certain linear hydrocarbons (C10-C40) were also quantified, but not systematically (except chlordecone) and at low or very low concentrations. Only references to the infectious organisms Clostridium perfringens and viable helminth eggs, chosen to judge the property HP9, were systematically exceeded for the former and on two samples for the latter. Since these references are not prohibited values in their context of use, and given the lack of feedback on this infectious hazard, the sediments of the Salt River cannot be considered hazardous with respect to HP9 and are therefore not to be considered as hazardous waste. 

Using the results  

Given the results, the biological quality of the sediments will have to be carefully scrutinised when considering their reuse. It may be necessary to monitor the parameters with the highest values before authorising certain uses, in particular those related to the production of food biomass on dredged materials. 

These sediments are often less contaminated than the soils likely to receive them in the case of dispersal along riversides, or have similar levels of concentration. Consequently, this type of reuse seems possible when it is necessary to raise the level of plots adjacent to the river, subject to compliance with the other provisions of the Water Act. 

The physico-chemical characteristics of the sediments also indicate that the preferred type of reuse should be landscaping rather than civil engineering, due to a very high fine fraction and high rates of organic matter (between 2.5 and 4.5%). At this stage, the methods for reusing these materials have not been identified and the process of prioritizing promising landbased reuses for dredged material in Martinique is ongoing. 

The partners  

  • DEAL Martinique  
  • Martinique Water Office 
Hazard properties presented in Regulation 1357/2014/EU

Hazard properties presented in Regulation 1357/2014/EU.