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Abstract
<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" dir="auto"
id="d5532216e140">The Amazon is the largest river by discharge volume and one of the
most biodiverse
biomes in the world. Lately, there has been a rapid increase of the urban population
in the region, which has been translated into a growing emission of organic contaminants
such as polycyclic aromatic hydrocarbons (PAHs) into surface water bodies. This study
provides the most comprehensive evaluation of the PAH contamination levels in surface
waters of the Amazon basin. We investigated the occurrence and potential sources of
16 priority PAHs and characterised their risks for freshwater ecosystems. For this,
we took 40 water samples from different sites along the Brazilian part of the Amazon
River, including three major tributaries, and smaller rivers crossing the main urban
areas. The results of this study show that PAHs are widespread contaminants in rivers
of the Brazilian Amazon. The sum of the total concentration of the 16 priority PAHs
reached values of 134 ng L-1 in the Amazon River, and 163 ng L-1 near densely populated
areas. On the other hand, the total PAH concentration was generally lower in the monitored
tributaries. In most samples, the contamination pattern was dominated by high molecular
weight PAHs, suggesting a major contribution of pyrogenic sources, although petrogenic
contamination was also present in some locations near urban areas. We assessed ecological
risks posed by PAH mixtures using a hazard index. The results indicated that PAH contamination
is not likely to pose direct toxic effects for Amazonian freshwater organisms, however
continued monitoring is recommended near densely populated areas.
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