Sediment Quality and Impact Assessment of Pollutants

Sediment Quality and Impact Assessment of Pollutants

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Sediment and Organisms as Marker for Metal Pollution

This ecosystem may be polluted by metal pollutants derived from human activities. Photo by Ong Meng Chuan. Rivers can transport metals into the marine environment, and the amount of the chemical element input to the oceans depends on their levels in the river sediments, water, suspended particulate matter, and the exchange processes that occur in the estuaries [ 10 ].

With recent industrialization and human activities Figure 2 that happen in the coastal region, these metals are continuing to be discharged to estuarine and coastal environment through rivers, runoff, and land-based point sources where the chemical elements are produced as a result of metal refinishing by-products. Example of human activities fishery industry in the Gulf of Morbihan, France. Metal concentrations in harbor or estuarine sediments usually are high due to significant anthropogenic contaminant loading carried by the upstream of tributary rivers and settled down at this area [ 11 , 12 ].

Sediment quality and impact assessment of pollutants

The sediments itself can serve as a metal pool that can release metals to the overlying water via natural or anthropogenic chemical and physical processes, causing potential adverse health effects to organisms that live at the ecosystems [ 13 , 14 ]. Moreover, marine organisms can uptake these chemical elements, which in turn enhances the potential of some elements entering into the food chain. Therefore, metal contaminations are considered by scientists as an environmental problem today in both developing and developed countries throughout the world [ 15 ]. Metals accumulate in the sediments through complex physical and chemical adsorption mechanisms depending on the nature of the sediment matrix and the properties of the adsorbed compounds [ 16 , 17 ].

Several processes had been identified for controlling the metal concentration in sediment, such as direct adsorption by small particle of clays, adsorption of hydrous ferric and manganic oxides which may also associate with clay fraction, adsorption of natural organic substances associated with inorganic particle, and precipitation as new solid phases [ 18 , 19 ]. With this unique characteristic, sediments are usually used as geo-marker for monitoring and identifying the potential pollution sources in aquatic environment.

These sediment analyses are an important tool for the determination of pollutants as they sink in the bottom through different chemical constituents and can reflect the pollutant proxy in the environment. In addition, the sediments act as a useful indicator of long- and medium-term metal flux in industrialized estuaries and rivers, and they help to improve management strategies as well as to assess the success of recent pollution controls [ 20 ].

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Therefore, sediments serve as a pool of metals that could be released to the overlying water from natural and anthropogenic processes such as bioturbation and dredging, resulting in potential adverse health effects toward surrounding organisms [ 22 , 23 ]. Besides that, it is necessary to determine the metal contamination in estuarine ecosystem because this area is the most productive ecosystem which serves as feeding area, migration route, and nursery area of many juvenile and adult organisms from freshwater and marine water ecosystem.

Due of these important to the ecosystem, effective remedial actions to minimize the pollution by metals need to be distinguished if pollution are expected occurs there [ 24 ]. Marine sediments Figure 3 , including materials originating from the terrestrial inputs, as well as atmospheric deposition and autogenetic matter from the ocean itself, preserve a continuous record of regional and even global environmental changes, which can be employed in metal pollution evolution [ 25 , 26 ].

Because of its unique characteristic, sediment always is considered as mirror of sedimentary environmental changes, which can reflect the biological, geodynamic, and geochemical processes of former conditions [ 27 , 28 ]. On the other side, environmental changes are not only driven by natural forces but also by anthropogenic effects by human [ 29 ].

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Some studies had concluded that the anthropogenic impacts on the environment have led to eutrophication process in coastal zone and offshore and the interaction of the natural force and human activities has exerted great effects on the whole environmental system[ 30 ]. Sediment sample usually used by researchers as geo-marker for pollution study. Sediments can pick up metals due to several chemical process and normally will settle down in marine aquatic environment. Because of this characteristic, sediment can act as an appropriate indicator to monitor the metal pollution.

In aquatic environment, these pollutants are originated from natural and anthropogenic sources in the same manner [ 31 ]; thus, scientists have difficulty to identify and classify the origin of these pollutants in the environment. Therefore, to overcome these obstacles, several scientists were using sediment fraction and characterized them into several sizes to normalize the metal concentration [ 31 , 32 ].

The rationale applying this approach is normally metals are associated with fine-grain fraction because this fraction has larger surface area and higher cation exchange capacity that can enhance metal adsorption [ 33 ].

With this characteristic, this fraction is suitable to determine the potential pollution in the sediment Figure 4. Fine-grain sediments have high surface area-to-grain size ratio which can accumulate more metals in the sediment. Because of their large adsorption capabilities, fine-grain sediments represent a major repository for metals and a record of the temporal changes in contamination. Thus, they can be used for historical reconstruction. Therefore, for better understanding about the metal behavior and distribution, it is important to distinguish between metals released from natural processes and those anthropogenic mainly introduced by human activities.

Marine sediments play a key role in the geochemical and biological processes of an estuarine ecosystem. In particular, these sediments act as sinks for toxic metals that enter the estuary. This sediment characteristic can regulate the concentration of these minerals and compounds in the water column [ 34 ]. Marine sediment also plays a very important role in the physicochemical and ecological dynamics of metals in marine aquatic ecosystems. The physicochemical nature of sediment-bound metals is important in the bioaccumulation of aquatic organisms such as fishes and shellfish.

Sediment quality has been recognized as an important and sensitive indicator or geo-marker of environmental pollution by various scientists [ 35 , 36 ] since sediments can act as an important sink for various pollutants, such as metals that had been discharged into the environment [ 37 , 38 ]. Besides acting as pollution indicator, sediments are also important in the remobilization process of contaminants in aquatic environment under favorable conditions through the interaction process between waste column and surface sediments.

Due to this process, scientists had developed several comprehensive methods to identify and assess the sediment contamination mainly to protect the marine aquatic organisms [ 39 ]. Over the last few decades, the study of sediment cores has shown to be an excellent tool for establishing the effect of anthropogenic and natural processes on depositional environments.

Meanwhile, sediment cores Figure 5 can provide chronologies of contaminant concentrations and a record of the changes in concentration of chemical indicators in the environment. During the early s, sediment profiles from depositional areas were used to trace human activity, witnessed by anthropogenic contamination like phosphorus [ 40 ], and later in the s, it was possible to distinguish radioactive isotope inputs due to nuclear tests.

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Metal accumulation rates in sediment cores can reflect variations in metal inputs in a given system over long periods of time. Hence, the study of sediments core provides historical record of various influences on the aquatic system by indicating both natural background levels and the man-induced accumulation of metals over an extended period of time. In addition, the dating of sediment cores using radioactive traces like Pb [ 41 ] permitted the precise quantification of the history of the inputs in a system [ 42 ].

Sediment core collected from mangrove ecosystem to study the metal proxy and sediment accumulation rate.

The absolute concentration of metals in marine sediments never indicates the degree of contamination coming from either natural or anthropogenic sources because of its grain-size distribution and mineralogy characteristic [ 43 , 44 ]. Normalization of metal concentrations to grain sizes, specific surface area, and reactive surface phases such as Li and Al is a common technique to remove artifacts in the data due to differences in depositional environments [ 45 , 46 , 47 ].

This method allows researchers to compare the contamination level directly even if the samples were collected at different locations. The most common normalization technique used is enrichment factor EF where this technique uses common elements such as Al, Li, and Fe as normalizer and index of geoaccumulation I geo or compares the normalized concentration to average crustal abundance data [ 47 , 48 ]. In order to examine to sediment status, the determined element concentrations normally were compared to the published background concentrations.

Literature data on average world shale or sediment cores or sediments from pristine such as undisturbed wetlands and non-industrialized regions were analyzed to establish the background values. However, to reduce the metal variability caused by the grain sizes and mineralogy of the sediments and to identify anomalous metal contribution, geochemical normalization has been used with various degrees of success by employing conservative elements [ 49 , 50 ].

Researchers have proposed various elements as normalizer, and these elements have the potential for the environmental studies. Some of them are lithium, Li [ 51 , 52 , 53 ]; aluminum, Al [ 54 , 55 ]; scandium, Sc [ 56 ]; cesium, Cs [ 57 , 58 ]; cobalt, Co [ 59 ]; and thorium, Th [ 60 , 61 ].

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Among all proposed normalizers, conservative elements, Li and Al, have been widely applied in marine and coastal study [ 62 , 63 , 64 ]. The concentration of metals in marine sediments cannot indicate the degree of contamination coming from either natural or anthropogenic sources because of grain-size distribution and mineralogy [ 44 , 65 ]. Normalization of metal concentrations to sediment size, specific surface area, and reactive surface phases such as Li and Al is a common technique to remove artifacts in the data due to differences in depositional environments [ 46 , 66 ]. This allows for a direct comparison to be made between contaminant levels of samples taken from different locations.

Based on the researches by several geochemists [ 67 , 68 ], if an EF value is between 0 and 1. If an EF is greater than 1. Similar to metal enrichment factor, I geo can be used as a reference to estimate the extent of metal pollution in sediments. The I geo value is calculated by using the following equation:. Factor 1. The upper continental crust values of the studied metals are the same as those used in the aforementioned enrichment factor calculation [ 71 ]. The highest class Class 6 reflects at least fold environment above the background value.

This assessment is a quick tool in order to compare the pollution status of different places [ 73 ]. PLI represents the number of times by which the metal concentrations in the sediment exceed the background concentration and gives a summative indication of the overall level of metal toxicity in a particular sample or location [ 74 , 75 ]. PLI can provide some understanding to the public of the surrounding area about the quality of a component of their environment and indicates the trend spatially and temporarily [ 76 ]. In addition, it also provides valuable information to the decision-makers toward a better management on the pollution level in the studied region.

PLI is obtained as contamination factor CF. This CF is the quotient obtained by dividing the concentration of each metal with the background value of the metal. The PLI can be expressed from the following relation:. The CF can be calculated from. The PLI value more than 1 can be categorized as polluted, whereas less than 1 indicates no pollution at the study area [ 77 , 78 ]. Over the last two decades, a considerable amount of research effort has been put into investigating sediment toxic threshold levels [ 79 , 80 ].

As a result there are now a number of international guidelines relating to toxic concentrations as determined by field and laboratory data. In their study, the toxicity range of these chemical pollutants in the sediments was estimated from experimental studies in the laboratory, observation, and measurement of these parameters in the field. Using this approach, scientists classified the toxicity of metals into effect range low ERL and effect range median ERM concentrations [ 79 ].

Nowadays, the rapid developments of computer technology and geographical information system GIS are receiving increasing interest in environmental geochemistry study [ 81 ]. This method is becoming popular nowadays in marine environmental pollution studies to graphically and digitally present the distribution of metals in marine environments by using GIS technique [ 82 , 83 ].

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