The pollution of the river must have had entrance route for heavy metals, probably through some feeding channels to the river. I want to know if the heavy metal enrichment is from effluent channeled into the river of probably through surface pollution by waste deposition etc.
Article A study of heavy metal pollution of Asa River, Ilorin. Niger...
To determine the possible origin of heavy metals in a determined mnatrix is not easy. There are different approachs that go from simple correlation tests between the metal concentrations in the possible sources and the sink to isotopic analysis but neither gives you 100% sure of the source of the heavy metals. Other possible approach is a geochemical analysis of the sink first layers (grain size, stable isotope, oxide composition etc) and comparasion with the same parameters in the possible sources.
Many rivers receive pollution from different sources (urban, industries, minig, runoff ) You must know the context in each case. Depending on where and when you take the sample you can identify some key compounds from a known source. Isotopic compositions and relationships can be indicative of different sources but they are not always easy to interpret. Mixing, interactions and transformations add complexity to this work.
There's technique called sequential extraction techniq, which somehow giv the origin of heavy metals either natural or anthropogenic. Sry if i answer it wrong
Our study in the Carson Basin of Nevada did not look at Hg sources. We did not have the funding to do such. But, HG sources run all along the Carson where smelters were located over a hundred years ago. Contaminant entrance into the river is mainly from spring runoff or when downpours occur. The Carson Basin is a terminal sink with no outlet. Therefore, the accumulation of the heavy metal enevitably occurs . The one reservoir on the lower Carson River also traps sediments, which accumulate over time. I wish we would of had the resources necessary to conduct a study on just how accumulation of Hg occurs, futher characterizing the important responses due to drought and more wetter conditions.
Origin of heavy metals into aquatic systems are diverse, may be as industrial effluents, mining activities,agricultural run off, fertilizers,dispersion ,atomic fall out, communal waste water discharge, volcanic eruptions, earth crust etc. It all depends on the environments lying within the vicinity of a particular water reservoir.,however, i do agree that sequential extraction techninque may give some conclusion but that alone may not be suffice,
A sequential extraction will be more important when risks are to be evaluated. I strongly suggest that a contour plot for each metal using samples from all different parts of the river will depict if there is a gradient in metal concentrations and if at some point in the river there is some diffuse entry of waste substances.
As colleagues already said, fingerprinting the source of metal contamination is not always easy. Looking at the work on the Asa river for example, the variations in concentrations are not really huge and it is difficult to highlight the anthropogenic sources. You can try two thinks at least. First, try to obtain particulate samples representative of the suspected sources: effluents, canals for agricultural areas or surface soils from the same areas, draining from urban areas. Second, normalize all your concentrations with one element not associated to anthropogenic inputs. Al is generally used, but you can also used Cs, Sr or Li, depending on what you get with the XRD technic. This normalisation could be efficient to better highlight spot sources, because it can also take into account grain-size or natural geochemical background variations. Sequential extraction could give you some informations, but they are quite difficult to perform accurately.
I believe that your question is focused more on metals in sediments but in the work I conducted in the Altamaha River System (GA, USA) I used biomonitor organisms (bivalves) to look for evidence of anthropogenic contamination of bioavailable metals. Because metal concentrations vary naturally in bivalve tissues, I used the statistical technique Hierarchical Linear Models to eliminate variability within and between sites caused by natural (rather than anthropogenic) variation. I think this statistical approach would also be useful for sediments, especially in a complex system like the Asa River.
Yup, sequential extraction is one hell method. this method do produce bias. Costly too. There are version of this method. I'm not sure if there is other method that produce similar result as this
You should read: Retention of resources (metals, metalloids and rare earth elements) by autochthonously/allochthonously dominated wetlands: A review
Jörg Schaller, Jan Vymazal, Carsten Brackhage
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