Copper, lead and cadmium loads and behavior in urban stormwater runoff in Curitiba, Brazil

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Abstract

We investigate the presence and behavior of Cu, Pb, and Cd in runoff waters from a residential area located in the city of Curitiba, Brazil. Samples were collected in twenty-one stormwater events in an intermediate traffic way located in the Bacacheri watershed. Metal concentrations were similar to range values compiled worldwide and followed the order: Pb>Cu>>Cd. Unit loads were estimated to the watershed, which cover an area of 30 km², revealing values of 1520, 950, 25 kg for Pb, Cu, and Cd, respectively. Among the three metals, lead showed the greatest affinity for the suspended solids (82%) followed by Cd (66%) and Cu (48%). Meanwhile, an association of the metals with the organic matter in the dissolved phase, following the order Cu>Pb>Cd. Metal loads and behavior in urban runoff also depends on factors such as the first flush and the dry period preceding a storm event.

Translated abstract

O objetivo deste trabalho foi avaliar a presença e o comportamento do Cu, Pb e Cd em águas de drenagem urbana na cidade de Curitiba, no Brasil. As amostras foram coletadas durante 21 eventos de chuva em uma avenida de tráfego médio. As concentrações dos metais foram similares àquelas descritas na literatura, seguindo a ordem Pb>Cu>>Cd. Uma estimativa da carga anual dos três metais para a Bacia do Rio Bacacheri, de 30 km², revelou valores de 1.520, 950 e 25 kg para Pb, Cu e Cd, respectivamente. O chumbo mostrou-se preferencialmente associado ao material particulado (82%), seguido do cádmio (66%) e do cobre (48%). Na fração dissolvida ficou evidenciada uma relação dos metais com a matéria orgânica dissolvida, seguindo a ordem Cu>Pb>Cd. As concentrações dos metais também variaram em função de fatores tais como o primeiro fluxo e o número de dias de estiagem que precedem um evento de chuva.

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River-derived humic substances as iron chelators in seawater

Regina Krachler, Rudolf Krachler, Gabriele Wallner … (2015)

The speciation of iron(III) in oxic seawater is dominated by its hydrolysis and sedimentation of insoluble iron(III)-oxyhydroxide. As a consequence, many oceanic areas have very low iron levels in surface seawater which leads to iron deficiency since phytoplankton require iron as a micronutrient in order to grow. Fortunately, iron solubility is not truly as low as Fe(III) solubility measurements in inorganic seawater would suggest, since oceanic waters contain organic molecules which tend to bind the iron and keep it in solution. Various iron-binding organic ligands which combine to stabilize dissolved iron have been detected and thoroughly investigated in recent years. However, the role of iron-binding ligands from terrestrial sources remains poorly constrained. Blackwater rivers supply large amounts of natural organic material (NOM) to the ocean. This NOM (which consists mainly of vascular plant-derived humic substances) is able to greatly enhance iron bioavailability in estuaries and coastal regions, however, breakdown processes lead to a rapid decrease of river-derived NOM concentrations with increasing distance from land. It has therefore been argued that the influence of river-derived NOM on iron biogeochemistry in offshore seawater does not seem to be significant. Here we used a standard method based on 59Fe as a radiotracer to study the solubility of Fe(III)-oxyhydroxide in seawater in the presence of riverine NOM. We aimed to address the question how effective is freshwater NOM as an iron chelator under open ocean conditions where the concentration of land-derived organic material is about 3 orders of magnitude smaller than in coastal regions, and does this iron chelating ability vary between NOM from different sources and between different size fractions of the river-borne NOM. Our results show that the investigated NOM fractions were able to substantially enhance Fe(III)-oxyhydroxide solubility in seawater at concentrations of the NOM ≥ 5 μg L− 1. Terrigenous NOM concentrations ≥ 5 μg L− 1 are in no way unusual in open ocean surface waters especially of the Arctic and the North Atlantic Oceans. River-derived humic substances could therefore play a greater role as iron carriers in the ocean than previously thought.