Heavy metal and PCB spatial distribution pattern in sediments within an urban catchment—contribution of historical pollution sources

Abstract

Purpose This work analyzes polychlorinated biphenyl (PCB) and heavy metal contamination in fluvial sediments and soils in an urban catchment, according to the geo-accumulation index and to soil and sediment quality guidelines. The catchment is located in Coimbra, Portugal, being affected by frequent flooding, and its main stream is a tributary to one of the major rivers in Portugal (Mondego). Given the presence of industrial activities over time, some inputs of pollutants are expected, but so far, the legacy of historic pollution in this catchment has not yet been investigated. Materials and methods Twenty-five samples were collected from nine sampling sites at the depths of 0-20, 20-40 and 40-60 cm (to provide a historic perspective) along longitudinal profiles (streamlines) and in soils downstream of pollution sources. These samples were analyzed for six heavy metals (Cu, Cr, Pb, Cd, Zn, Ni), organic carbon, pH and ten PCBs (IUPAC numbers 28, 30, 52, 101, 138, 153, 166, 180, 204, 209). Results and discussion Total PCB concentrations ranged 0.47-5.3 ng g −1 dry weight (dw), and levels increase from the bottom to the top layers, suggesting an increased input over the last 100 years. PCB congener distribution shows the dominance of hexachlorobiphenyls, especially PCB138, suggesting the existence of local sources. PCB levels did not exceed sediment quality levels, placing sediments/soil under class 1 (not contaminated) or class 2 (trace contamination) with respect to PCB. All six metals exceeded the lowest effect level for sediment quality criteria, and three (Cd, Pb and Zn) largely exceeded the clean levels for dredged materials, placing sediments in class 5 (heavily contaminated). Sampling site S1 presented the highest concentrations of Zn, Pb and Cd, and historic vehicle traffic was identified as the most likely source, given the vertical and horizontal profiles.Conclusions High levels of Pb, Cd and Zn were found in fluvial sediments at some locations of the Loreto catchment, likely from historic traffic sources. This urban area is frequently affected by flooding events and is currently being subject to urban redevelopment. During these events/actions, historic pollutants in the sediments might surface and be redistributed, impacting the downstream ecosystem of the major Mondego River or increasing the risk of exposure of the urban population.

Understanding the Role of Organic Matter Cycling for the Spatio-Temporal Structure of PCBs in the North Sea

“…These distribution changes were in accordance to findings by [26]. Two aspects of the spatial distribution of surface PCBs are the anthropogenic PCB production and the associated discharges from land [24,26,[64][65][66][67][68]. Though their production is currently banned by the Stockholm Convention (http://www.pops.int/access 09.12.2019), these contaminants are still entering the environment via leaching and weathering from already existing products.…”

Degradation in urban areas

“…Pollutants deriving from urban areas include heavy metals [31], PCBs [47], nutrients [48], pesticides [44], pharmaceuticals [49] and faecal coliforms [50]. Sources of water pollution in urban areas can include (i) industrial processes and spills [51], (ii) untreated solid waste disposal and leachate from landfills [52], (iii) wastewater contamination from septic tanks, leakages in sewage systems and inefficient wastewater treatment [53], (iv) stormwater runoff [31,54], (v) lawns and gardens maintenance due to inappropriate fertilization and irrigation [55], (vi) soil erosion [56], and (vii) atmospheric deposition [30].…”

“…Urban streams, however, typically display reduced baseflow due to lower groundwater contributions [38,43], although sometimes water and sewer leakages within artificial drainage systems may enhance this streamflow component [44].Urban areas comprise varying spatial mosaics of paved/sealed surfaces and green areas.Different combinations and spatial arrangements of impervious and pervious surfaces greatly affect the rainfall-runoff process, as well as the connectivity between land surface and the drainage network, and thus the speed and magnitude of runoff delivery to the stream[17,42]. For example, Ferreira et al[47] recorded response times three times shorter in urban sub-catchments with continuously built-up areas located downslope, than with M A N U S C R I P T A C C E P T E D 9 peaks and total streamflow than piping into adjacent areas of permeable soil[40].Conventional piped drainage leads to four times greater runoff than a swale drainage system[19].…”

Heavy Metals in Sediments of Urban Streams: Contamination and Health Risk Assessment of Influencing Factors

“…Contemporary studies [2,[5][6][7][8][9][10] revealed that storm water run-off carried metals originating from a variety of everyday activities associated with tire wear, corrosion, roof run-off and fuel combustion products. It is well established that run-off from urbanized catchment is abundant in HMs [11][12][13]. However, little is known as regards the influence of the run-off from urbanized catchment composed of soft, natural surfaces (forest, lawns, gardens) vs run-off from 2 of 14 paved surfaces (roads, sidewalks, squares, fuel stations) on the metals levels in the run-off receivers.…”