Only a few studies have reported on the evaluation of analytical method
performances such as recoveries and LOQ (Coogan et al. 2007; Huerta et al.
2016) or matrix effects (Headley et al. 2001; Ruhí et al. 2016). The relatively low
amounts of contaminants sorbed on biofilms (trace levels) and the limited biomass
collected (often <200 mg) mean that LOQ values are generally in the same order of
magnitude as the measured concentrations. As an example, Huerta et al. (2016)
reported LOQs from 0.07 to 6.7 ng g
À1 for pharmaceuticals (in 200 mg of
phototrophic biofilms), whereas most of the values measured in biofilm samples
were between 1.8 and 22 ng g
À1 . Matrix effects due to the specificity of the analyzed
biofilm are also under-addressed. To illustrate, when Huerta et al. (2016) compared
analyses of biofilm extracts against the initial solvent mixture spiked with different
contaminants at the same concentration level, they observed either ion suppression
or ion enhancement depending on organic contaminant, thus demonstrating that
concentrations values in biofilm extracts can be biased (i.e., over- or underestimated)
due to matrix effects. For quantification purposes, matrix-matched calibration
together with added internal surrogates (ideally labeled compounds) is thus advocated to compensate for these matrix effects (Huerta et al. 2016; Ruhí et al. 2016).
3 Contaminant Bioaccumulation in Microbial Biofilms
from Freshwater Ecosystems
Microbial biofilms can adsorb and accumulate both metals and organic contaminants. The nature of the contaminant, the surrounding environmental conditions, and
the type of biofilm have all been found to influence contaminant bioaccumulation
patterns. Note that bioaccumulation cannot be apprehended in the same way in
periphytic biofilms, which are easily detached from their growth substrate, nor in
biofilms strongly attached to leaf litter or fine detritus in sediments, which makes it
difficult to specifically quantify the contaminants accumulated in the microbial
biomass.
3.1 Contaminant Bioaccumulation in Periphytic Biofilms
Natural periphytic biofilms have been found to host a large variety of contaminants.
Current knowledge on bioaccumulation in periphyton is illustrated and discussed
here based on a meta-analysis of 24 published studies (Table S1). The data collected
gather field and laboratory experiments including simultaneous quantification of
contaminants in water and periphyton (Fig. 4) with biofilms sampled at various
stages of maturity. Most of this data comes from chronic exposures, but some pulsed
exposures are also included. To estimate uptake efficiency, bioconcentration factors
(BCFs) were used as a proxy and were calculated as the ratio between the concentration measured in the biofilm and the dissolved concentration in the medium
126
C. Bonnineau et al.
performances such as recoveries and LOQ (Coogan et al. 2007; Huerta et al.
2016) or matrix effects (Headley et al. 2001; Ruhí et al. 2016). The relatively low
amounts of contaminants sorbed on biofilms (trace levels) and the limited biomass
collected (often <200 mg) mean that LOQ values are generally in the same order of
magnitude as the measured concentrations. As an example, Huerta et al. (2016)
reported LOQs from 0.07 to 6.7 ng g
À1 for pharmaceuticals (in 200 mg of
phototrophic biofilms), whereas most of the values measured in biofilm samples
were between 1.8 and 22 ng g
À1 . Matrix effects due to the specificity of the analyzed
biofilm are also under-addressed. To illustrate, when Huerta et al. (2016) compared
analyses of biofilm extracts against the initial solvent mixture spiked with different
contaminants at the same concentration level, they observed either ion suppression
or ion enhancement depending on organic contaminant, thus demonstrating that
concentrations values in biofilm extracts can be biased (i.e., over- or underestimated)
due to matrix effects. For quantification purposes, matrix-matched calibration
together with added internal surrogates (ideally labeled compounds) is thus advocated to compensate for these matrix effects (Huerta et al. 2016; Ruhí et al. 2016).
3 Contaminant Bioaccumulation in Microbial Biofilms
from Freshwater Ecosystems
Microbial biofilms can adsorb and accumulate both metals and organic contaminants. The nature of the contaminant, the surrounding environmental conditions, and
the type of biofilm have all been found to influence contaminant bioaccumulation
patterns. Note that bioaccumulation cannot be apprehended in the same way in
periphytic biofilms, which are easily detached from their growth substrate, nor in
biofilms strongly attached to leaf litter or fine detritus in sediments, which makes it
difficult to specifically quantify the contaminants accumulated in the microbial
biomass.
3.1 Contaminant Bioaccumulation in Periphytic Biofilms
Natural periphytic biofilms have been found to host a large variety of contaminants.
Current knowledge on bioaccumulation in periphyton is illustrated and discussed
here based on a meta-analysis of 24 published studies (Table S1). The data collected
gather field and laboratory experiments including simultaneous quantification of
contaminants in water and periphyton (Fig. 4) with biofilms sampled at various
stages of maturity. Most of this data comes from chronic exposures, but some pulsed
exposures are also included. To estimate uptake efficiency, bioconcentration factors
(BCFs) were used as a proxy and were calculated as the ratio between the concentration measured in the biofilm and the dissolved concentration in the medium
126
C. Bonnineau et al.