Environmental Engineering Reference
In-Depth Information
products [6]. This signiicant increase in the ENP-containing consumer products has
increased the chances of their inadvertent release in the surface and subsurface environ-
ment through landills and other waste-disposal methods [7]. The “cradle to gate and
grave” paradigm is also relevant to the release of ENPs into the environment at any stage
of their life cycle, viz. production, transportation, consumer usage, and disposal.
It is also known that ENPs have excess energy at the surface, which makes particles
highly reactive, mobile, thermodynamically unstable, and thus a very special class of pol-
lutant [8]. It is also likely that some of the ENPs released into the environment induce a toxic
response both in lower and higher trophic organisms of the aquatic ecosystem. Evidence is
accumulating that ENPs cause toxicity to microbes, invertebrates, ishes, lower vertebrates,
and others, the key components of the aquatic ecosystem. Studies have shown that ENPs
adversely affect the microbes (
Escherichia coli
,
Pseudomonas aeruginosa
, and
Streptococcus
aureus
) that are responsible for the maintenance of environmental health [9-13]. These
observations indicate the possibility that the release of ENPs may be detrimental to bio-
geochemical processes in soil, such as carbon or nitrogen cycling. It is also likely that the
ENPs can directly interact with the food web at different trophic levels and disturb the
ecological balance. Therefore, organisms, especially those that interact strongly with their
immediate environment, could be more at risk to the direct exposure of ENPs [14]. The
biomagniication of ENPs across the genera is also a major concern.
Moreover, the impact of ENPs on aquatic ecosystems is governed by their distribution,
which depends on various factors such as Brownian motion, inertia, gravitational inlu-
ences, thermal inluences, pH, and ionization [15]. The possibility of the high mobility
of ENPs in water can lead to contamination of the lora and fauna. This may also result
in the transfer of ENPs in the food chain, leading to the generation of nonbiodegradable
pollutants [16]. Also, ENPs can affect the bioavailability of the other toxicant/pollutant
by facilitating their transport [8,17]. ENPs thus elicit a negative impact on the physical,
chemical, and biological strata of the aquatic ecosystem. Hence, to minimize the exposure
in ENPs and thereby adverse effects on the aquatic ecosystem, it is imperative to consider
the following issues: (i) bioavailability of ENPs in aquatic systems, (ii) methodological and
metrological approaches for the detection and quantiication of ENPs in environmental
samples, and (iii) approaches and knowledge gaps in aquatic toxicity.
5.1 Bioavailability of ENPs in Aquatic Systems
The availability and uptake of ENPs to the cell is an important factor that can provide rel-
evant information pertaining to their adverse effects on cellular systems. There have been
a number of recent reports that have addressed the fate and effects of ENPs in the environ-
ment [3,18-21]. Many of these reports speciically refer to the potential impacts of ENPs on
aquatic environments, since surface waters receive pollutants and contaminants, includ-
ing ENPs from many sources, and act as reservoirs and channels for many environmental
contaminants [3]. Understanding the potential impacts and toxicity of ENPs on the organ-
isms within these environments is critical. At present, there is little information about the
number of ENPs that enter aquatic environments and their routes of entry. The potential
routes include atmospheric deposition, leaching from soil, direct input from wastewater
discharges, and groundwater reservoirs [18]. Evidence for possible contamination of water
sources with nanoparticles has already been reported by Mueller and Nowack [22]. They
