301
11.6.1 Bioavailability
According to Peijnenburg (2015), bioavailability is the chemical fractions which is
accessible or made accessible for uptake causing positive or negative effects in
organisms (Peijnenburg et al. 2015). In addition, Ortega-Calvo et al. (2015) defined
bioavailability as the component that includes the dissolved fractions of a chemical
in soil, whereas bioaccessibility comprises the fraction which may be bioavailable
in the long term (Ortega-Calvo et al. 2015). Gaiser et al. (2012) viewed bioavailability in terms of nutritional efficiency, that is, the portion that is taken up, incorporated and utilized for storage and metabolism (Gaiser et al. 2012). The bioactive
fraction, in totality, is related to the targeted organelle or particle and the interactions between particles, and thus, to the physiological and biochemical reactions
generated and generally termed as biomarkers. It has been observed that engineered
nanomaterials in marine ecosystems have a tendency to aggregate more as compared to aqueous freshwater because of surface charge screening in seawater due to
high salts, thus, lessening the bioavailability of nanomaterials. Although the bioavailability is decreased, the cited works indicated that engineered nanomaterials
are still bioavailable to organisms in marine systems (Table 11.2).
11.6.2 Bioconcentration
Bioconcentration is the procedure through which toxicants are passively absorbed
by the living organisms from the environmental matrix exclusively through respiratory and/or dermal surfaces. For quantitatively measuring this process, bioconcentration factor (BCF) is conventionally calculated which is expressed as the ratio of
the particle concentration in an organism to that in exposure medium (usually water
or medium). BCF, expressed in terms of L kg
−1
, are usually expressed as chemical
mass per L and chemical mass per kg biomass, respectively. BCF is measured at its
steady state and is a net effect of uptake and elimination processes, taking care of
metabolic transformation, fecal egestion, gill elimination, and growth dilution. The
approximation of BCF can invite a few ambiguities as literature reports are either
merely abstractive or it is difficult converting to BCF used for assessment. For
example, the mean log BCF values for daphnids in case of many ENPs are quite
broad, and vary from 3.16 to 5.64. On the other hand, the engineered nanomaterials
mean log BCF values in fish varies from 1.27–2.87, which are 1–2-folds lesser than
those of daphnids (Hou et al. 2013). However, bioconcentration can only be determined in controlled environmental settings.
11 Environmental Impact and Econanotoxicity of Engineered Nanomaterials
11.6.1 Bioavailability
According to Peijnenburg (2015), bioavailability is the chemical fractions which is
accessible or made accessible for uptake causing positive or negative effects in
organisms (Peijnenburg et al. 2015). In addition, Ortega-Calvo et al. (2015) defined
bioavailability as the component that includes the dissolved fractions of a chemical
in soil, whereas bioaccessibility comprises the fraction which may be bioavailable
in the long term (Ortega-Calvo et al. 2015). Gaiser et al. (2012) viewed bioavailability in terms of nutritional efficiency, that is, the portion that is taken up, incorporated and utilized for storage and metabolism (Gaiser et al. 2012). The bioactive
fraction, in totality, is related to the targeted organelle or particle and the interactions between particles, and thus, to the physiological and biochemical reactions
generated and generally termed as biomarkers. It has been observed that engineered
nanomaterials in marine ecosystems have a tendency to aggregate more as compared to aqueous freshwater because of surface charge screening in seawater due to
high salts, thus, lessening the bioavailability of nanomaterials. Although the bioavailability is decreased, the cited works indicated that engineered nanomaterials
are still bioavailable to organisms in marine systems (Table 11.2).
11.6.2 Bioconcentration
Bioconcentration is the procedure through which toxicants are passively absorbed
by the living organisms from the environmental matrix exclusively through respiratory and/or dermal surfaces. For quantitatively measuring this process, bioconcentration factor (BCF) is conventionally calculated which is expressed as the ratio of
the particle concentration in an organism to that in exposure medium (usually water
or medium). BCF, expressed in terms of L kg
−1
, are usually expressed as chemical
mass per L and chemical mass per kg biomass, respectively. BCF is measured at its
steady state and is a net effect of uptake and elimination processes, taking care of
metabolic transformation, fecal egestion, gill elimination, and growth dilution. The
approximation of BCF can invite a few ambiguities as literature reports are either
merely abstractive or it is difficult converting to BCF used for assessment. For
example, the mean log BCF values for daphnids in case of many ENPs are quite
broad, and vary from 3.16 to 5.64. On the other hand, the engineered nanomaterials
mean log BCF values in fish varies from 1.27–2.87, which are 1–2-folds lesser than
those of daphnids (Hou et al. 2013). However, bioconcentration can only be determined in controlled environmental settings.
11 Environmental Impact and Econanotoxicity of Engineered Nanomaterials