[3] PICT can be used for linkage between cause (exposure) and effect of the toxicants due to the structure of a community that has survived the event, also known as toxicant-induced succession (TIS).
A first step would then be to use a model toxicant from a class of pollutants (selected on the basis of their co-tolerance properties) in order to limit the number of suspect pollutants in the ecotoxicological assessment of an environment [2] For example, a PICT study on soil in microcosms amended with organic manure observed co-tolerance only between antibiotics of the same group (oxytetracycline and tetracycline), as expected from their identical mode of action.
Their results demonstrate the value of combining the PICT approach with the use of passive sampler extracts to establish causality between in situ exposure to complex mixtures of micropollutants and ecotoxic effects on autotrophic and heterotrophic microbial communities.
Assessing pollution-induced community tolerance can be done utilizing in situ techniques, many of which involve the use of known or created chemical exposure gradients.
Of particular note at this site is the study conducted by Pesce et al. (2016)[28] during three consecutive years (2009–2011): The authors monitored the decrease in tolerance of periphyton to diuron (herbicide applied in vineyards and banned since 2008) downstream of the river crossing this wine-growing watershed.
Their results showed a direct link between the evolution of an agricultural practice (here the banning of diuron) and ecological changes in the river (through the loss of tolerance measured by the PICT).
Total Biomass decreased at the outset of the trials involving high concentrations of Cu indicating that Community Tolerance was increased due to direct mortality of the sensitive species.
[30] The in situ study of Bérard & Benninghoff, (2001)[31] in enclosures repeated over several years in the lake of Geneva, showed that the tolerance of phytoplankton to the herbicide atrazine (photosynthesis inhibitor) varied according to the seasons during which the experiment was carried out.
These changes in tolerance for the same toxicant and at the same concentration (10 μg/L) were probably linked to the initial compositions of the algal and cyanobacterial communities and to environmental factors associated with seasonal parameters (temperature, light, nutrients, etc.).
[38][39][12] In the context of agricultural contamination, Bérard et al. (2004)[40] validated the PICT tool (by measuring photosynthetic activity) for atrazine tolerance on edaphic microalgae, comparing soils of conventionally and organically farmed corn fields.
Changes in taxonomic structure of diatom communities sampled from soils under both types of farming practices, as well as nanocosm experiments, confirmed the selective effect of atrazine.
Experimental investigation of PICT is performed to eliminate factors other than pollution that may affect community structure and ecophysiology,[1] or on the contrary to study them (by controlling them).
This work highlighted the high toxicity of Irgarol (compared to atrazine having the same site of action, and presenting a co-tolerance) on periphyton and phytoplankton and its potential for selection pressure at existing concentrations in the lake.
There are a variety of methods for laboratory testing PICT, but a general format includes sampling, a bioassay, and an analysis of community structure.
For 14 days communities were allowed to establish on discs set up in laboratory aquariums which were continuously mixed and inoculated with algae from a pond.
[50] Generally one samples the soil with its intrinsic heterogeneity and components other than microorganisms (minerals, organics ..), which increases measurement difficulties and biases related to contaminant bioavailability.
[21][49] Since the work of Blanck et al. (1988), other endpoints have been tested such as: induced fluorescence,[52] PAM fluorimetry,[53][54][42] leucine incorporation and eco-plates,[55][56][57] microbial respiration,[58][38][35][59] enzyme activities,[60][61][42] potential ammonium oxidation assay[57]...
[62][63][2] Community structure of the samples is analyzed to check for a correlation between species prevalence and long-term contaminant exposure.
Samples are taxonomically classified to determine the composition and species diversity of the communities that established over the long term exposures.