Trace And Heavy Metals In The Sediment Of The Brisbane River System

Large populations of humans tend to live near bodies of water. Because of these dense populations, water quality is an issue in these areas. Due to natural and anthropogenic changes, water quality can become poor (Duodu et. al). Contaminants negatively affect water quality from many sources such as disposal of liquid effluents, runoff carrying harmful chemicals that may be urban, industrial, or agricultural in origin, and atmospheric deposition. These contaminants will affect the sediments, which can cause an abundance of environmental issues (Mucha et. al). The Brisbane River is an example of a fluvial system that contains these pollutants in its sediment, and may pose an ecological risk (Duodu et. al). Through the discussion of three different case studies involving the Brisbane River system, the extent of the metal pollution in this area can be better understood.

The Brisbane River is located in Southeast Queensland, Australia. This river supports the population of this large city and is the most urbanized fluvial system in southeastern Queensland. Throughout the years, this river has received treated sewage from eight different water treatment facilities. (Duodo, 2016). The Brisbane River has an estuary that opens up into an important port, Moreton Bay. The estuary that leads to this port is very industrialized, which causes waste from many sources, such as oil refineries and a sewage treatment plant to enter the channel. This estuary also receives pollution from the city of Brisbane because of its close proximity (Mackey et. al).

Since the Brisbane River has many anthropogenic influences, major and trace metals may be found in the sediment (Duodu et. al). Metals pollutants in the sediment can show major environmental change since they cannot be broken down (Arnason & Fletcher). Some of the human made sources of these trace metals are maritime and port activities, petroleum refining and storage, manufacturing, chemical processes, landfills, agriculture, intense fertilizing, and the effects of urban centers (Cox et. al). Other human influences such as closing lagoons, extending harbor areas, deepening navigation channels, and channelization of rivers can also add to the amount of contaminants. These pollutants can have various effects on the environment. Trace metals can be altered to toxic organo-metallic compounds by biologically mediated reactions in the sediment (Salomonds & Forstner). This poses an ecological risk because heavy metals in sediment can travel back to the sediment-water environment due to diffusion, sediment resuspension, or biological activity. Once this is in the sediment-water interface, it may enter the food web, and cause damage to the ecosystem (Arnason & Fletcher).

A 2016 study from the Queensland University of Technology examined the source, distribution, contamination, and ecological risk of the heavy metals in the Brisbane River. Twenty-two different sites were sampled to include different land use types and urbanization levels. These sites were then put into four categories: rural, residential, commercial, and industrial. At each site, a sample within the first 0-3 centimeters of depth was taken, and were stored in a lab at -20°C until they were analyzed. A sample from an area with little anthropogenic influence was also collected to be used as a background sample. To prepare the samples for analysis, Germanium (II) oxide was used as an internal standard and added to sediment samples. Ethanol was added to the Germanium and sediment mixture, and was then milled and homogenized. Next, the mixture was dried in an oven and a 1 gram sediment sample was pressed into a pellet. The pellets were measured by the laser ablation inductively coupled plasma mass spectrometry technique (LA-IDP-MS). After the data was collected, the average and standard deviation of the metal concentrations was calculated (Duodo et. al).

The LA-IDP-MS technique created data that helped interpret trends within each sampling location. By identifying these trends, the data was then put into groups by their similarities and their sources. Once the samples were grouped, sediment quality indices were applied to determine if the contaminants would be toxic in their current concentrations. The data was then evaluated by source identification, contamination factor, enrichment factor, index of geo-accumulation, modified degree of contamination, modified pollution index, sediment quality guidelines, potential ecological risk factor, and modified ecological risk index. Through this evaluation, it was found that the metals studied were stable across sampling sites and periods, but variation occurred in the source. The three sources identified were marine sand intrusion, mixed lithogenic sand intrusion, and transport related. Through the contamination factor, enrichment factor, index of geo-accumulation, modified degree of contamination, pollution index, and modified pollution indices, it was found that there was contaminated sediment. The contaminated sediment was from sites that were near bridges, indicating a transport related origin. Quality guidelines were used to determine that Ag, Cr, Cu, Ni, Pb, and Zn may rarely cause biological effects. Also, the guidelines showed that Hg will commonly cause effects. Because of this, the ecological risk index showed a moderate to considerable risk factor, while the modified ecological risk index showed a moderate to high risk. These results identify metals in the sediment as a potential ecological risk, and further study should be conducted to understand the extent of the pollution (Duodo et. al).

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The next study was conducted by the Centre for Biological Population Management and the Centre for Industrial and Developmental Chemistry at the Queensland University of Technology. This study investigates the nutrient and heavy metal levels in the mangroves of Moreton Bay, which is where the Brisbane River opens up to. This study site is approximately 3 kilometers from the river mouth, and is near an important port. The area of study is only a few kilometers away from the city of Brisbane so it is very industrialized, and receives pollution from oil refineries and sewage treatment facilities. Only a few mangroves are left in this area, since most of them have been cleared due to human activity. The area of interest is one of the few mangroves left in the area and is of importance because they are breeding and feeding areas for local fish and prawns. Many of the sediments from the Brisbane River end up in these mangrove sediments, so it is important to identify potential ecological risks within the communities. To conduct this study, sediment samples were taken every 50 meters throughout a mangrove area. Each sample was collected from a depth of 2 centimeters and put into 250 ml glass jars. The samples were then acid soaked, rinsed, and stored on ice until they were analyzed in a lab. Once in the lab, the samples underwent a metal and nutrient analysis, and a duplicate analysis was conducted on 10% of the samples. The metal analysis was performed by ICP spectroscopy, and the nutrients were analyzed by extracting the Nitrogen species. To insure accuracy of both analyses, the samples were compared to a reference material. The results of this study showed that the nutrient levels in this mangrove were high, which may be caused by the sewage treatment facility that is nearby. Also, it was found that the levels of heavy metals in the sediment were also high, with the highest levels being towards the seaward edge of the mangrove. These higher levels can be attributed to industrial and urban influences. In conclusion, nutrient and heavy metal levels have increased in this area due to anthropogenic influences, but more data and research is needed for a better evaluation of these changes (Makey et. al).

The last study was conducted through the Sydney Water Board and it investigated the geochemistry and dispersion pattern of heavy metals in the coastal sediments, soil, and water in the Kendron Brook flood plain in Brisbane, Australia. This area is part of the Brisbane River floodplain and the Kendron brook, artificial drains, and canals drain into the area. In this study, 32 surface water samples were collected in depths of 0.5 meters below the surface. Sediment samples were also taken by a grab sampler, along with sediment cores. All three sample types were taken along the floodway channel, and the sediment and soil were stored in cool temperatures until they reached the lab for testing. To analyze the water samples, 75% of each water sample was put through a filter system and then the dissolved solids and soluble phases of heavy metals were determined. The sediment samples were filtered, separated with a centrifuge, dried, weighed, digested by hydrochloric acids, and then were put through a spectrometer to determine their mineralogy. Lastly, the soil samples were tested on grain size, pH, and mineralogical identification. Through these analyses, it was found that clays, Fe-Mn oxides, and humic acids in the soil samples were main adsorbents of heavy metals. The concentration of heavy metals depended on climatic and hydrodynamic conditions. Also, the concentration of heavy metals in these sediments occurs from wetting and drying of the soils. For the sediments, most of the heavy metal concentrations were residual. Most of these metals were bound to their organic phase, except for Cu and Cd which were apparent due to the surrounding area. However, these metal concentrations were considered high when compared to the world shale standard. Since the soils in this area are slightly acidic, humic acids that absorb the heavy metals form gels that hold metals in a concentrated, stable state. The metals will stay in this state until the water table rises during the wet seasons, which increases mobility of the heavy metals. This is because more favorable Eh conditions occur for metal oxidation when the water table rises. These seasonal changes indicate that the mobility of heavy metals in this area are due to salinity, formation of organic complexes, redox conditions, and pH. Through this study, it is learned that there are many factors that can contribute to the concentration of heavy metals in soil and sediment, and that seasons can affect mobility as well. This study suggests the need for future research to better understand coastal hydrodynamics and geochemical reactions. This will help solve future environmental issues regarding metal concentrations from natural and anthropogenic sources (Arakel & Hongjun).

The three articles examined metal pollutants in three different locations that involved the Brisbane River. The strengths of these studies were that when they examined the concentrations of metals in their samples, they compared it to either a background sample with little anthropogenic influence, or they compared it to guidelines for sediment quality. This is beneficial because it allows others to understand if a concentration of metal in a sample is to be of ecological concern or not. Also, the three studies each investigated a different aspect of the area to determine how contaminated sediment is distributed. The first study by Duodu, Goonetilleke, and Ayoko collected their sediment samples at various urbanization levels along the Brisbane River (Dudodu et. al). In the next study by Mackey, Hodgkinson, and Nardella studied the mangrove area of Moreton Bay which is where the Brisbane River opens up to (Mackey et. al). Lastly, Akrakel and Hongjun studied one of the floodplains of the Brisbane River (Arakel and Honjun). Lastly, the studies by Duodo et. al and Arakel and Honjun express the need for future research on this topic. With thorough data, multiple study sites, and the expression of a need for future research, these studies contain very valuable strengths.

The three studies had very few weaknesses. One weakness was identified in the studies from Duodo et. al and Arakel and Hongjun. In these two studies, some of the methods and results were hard to follow. For example, in Duodu et. al., they tested their sediment samples with many different factors such as source identification, contamination factor, enrichment factor, index of geo-accumulation, modified degree of contamination, modified pollution index, sediment quality guidelines, potential ecological risk factor, and modified ecological risk index (Duodu et. al). Although these indices came together to form a complete conclusion, it may have been beneficial to test similar topics separately for a more specific evaluation of data, such as the source identification. In Arakel and Hongjun, they tested water, soil, and sediment together for heavy metal concentration, when it may have been beneficial to study soil and sediment together (Arakel & Hongjun).

In summary, three studies were conducted on trace and heavy metal concentrations in the Brisbane River system. These studies researched many different aspects of the river system such as the Brisbane River itself, a mangrove in Moreton Bay, and one of the Brisbane River’s flood plains. These studies found that these areas do have trace and heavy metals in the sediments, and some of the higher levels that were found may pose an ecological risk to the surrounding environments (Duodu et. al), (Mackey et. al), (Arakel & Hongjun). The presence of trace and heavy metals in these sediments can be ecologically harmful because they may enter the water if diffusion, sediment resuspension, or biological activity occurs. Once these toxic metals have entered the water, they can also enter the food web and cause damage to the surrounding biology (Arakel & Hongjun). Trace and heavy metals enter fluvial systems due to many factors such as maritime and port activities, petroleum refining and storage, manufacturing, chemical processes, landfills, agriculture, intense fertilizing, and the effects of urban centers as well as some natural processes (Cox et. al). Metallic contaminants are more prevalent in urban and industrialized areas because of these anthropogenic activities. (Duodu et. al). Because of the studies that have been reviewed, methods for identifying these contaminants have been established, concentrations of harmful trace and heavy metals have been identified, and potential future research to help identify and solve the problem of these pollutants has been deemed essential to avoid potential ecological harm.