Testing sediments is one of the best approaches to obtain historical information on the pollution of an area because they represent the environmental matrix that gathers both materials coming from the rocks in the emerged land and spilling into the environment caused by human activities.
Sediments: what is the contamination?
Sediments represent the environmental sector identifiable as the final collection point of rocky materials deriving from the rocks in the emerged land and how much was spilled into the environment by human activities. Anthropogenic sources can pollute the aquatic environment: some contaminants –which in water are only found in traces–, can accumulate in sediments and their concentrations may increase over time. Later, contaminants can re-circulate in the environment, by transfer in the above water column.
The danger of polluted sediments lies in the fact that any contamination has repercussions on benthic organisms and other organisms that come into direct or indirect contact with them, with consequences that affect the entire food chain.
Sediments can be used in different ways, especially for nourishment (for example, of shorelines) and for the brick industry: carrying out the analysis is therefore important to acquire knowledge about the degree of pollution of the marine environment (or rivers, lakes, etc.) and for the purpose of the possible re-use or in general of the management of dredged sediments.
Sediments contamination: many important analyses to take into consideration
Chemical substances of anthropogenic origin can enter the aquatic environment and then settle in the sediments through specific sources, such as an industrial or civil drain, contaminated sites or accidental spills; they can also derive from widespread sources, such as leaching, erosion of agricultural land treated with pesticides and atmospheric deposition. Among the main pollutants, there are heavy metals, dioxins, PCBs, hydrocarbons, pesticides. Some of these are POPs (Persistent Organic Pollutants), characterized by high lipoaffinity, semi-volatility and resistance to degradation. In typical environmental conditions, they tend to concentrate, thus reaching potentially significant concentrations from the health and environmental points of view.
In addition, microbiological contamination has to be taken into account: the microbiological analysis of sediments is often carried out to identify pollutants deriving from sewage discharges or in general from wastewater treatment.
Parameters such as macroscopic description, humidity and pH of the sediment help to classify the sediment in the environment from which it was taken. Granulometry –a test performed thanks to a laser granulometer– is one of the key factors in the field of sedimentology because the size of the particles precisely influences the ability to retain water, nutrients and contaminants.
Toxicological tests give us an idea of sediment contamination since the possible inhibition of algal growth or other parameters on different organisms indicate a situation that is possibly harmful to the ecosystem.
Sediments testing: possible applications
The following case studies can be an example of the application of sediments testing with the aim to better discover their characteristics and possible uses.
According to the level of contamination, the sediment can be re-used or considered a waste: tests performed on dredged sediments aimed at characterizing waste with analytical profiles that allow defining their final disposal or recovery plant.
In the eco-toxicological framework, bio-indicator tests (for example, mussels) play an important role, as bio-accumulators can outline a significant picture of the contamination of both sediments and water column, thus allowing evaluations on the bioavailability of toxic substances and their transfer into the food chain.