4.2 The WOE Methodology: Towards an Index of Ecological
Disturbance
The WOE methodology consisted in gathering the selected parameters into four
LOEs: sediment and water chemistry (contamination level analysis), contaminant
bioavailability (bioaccumulation levels in caged gammarids), biomarker responses
(in gammarids) and bioassay responses (on sediment and water samples). A hazard
quotient (HQ) was then calculated for each LOE and reported in an evaluation grid
for a rapid and clear hazard classification (i.e. ranging from absent to severe). An
overall risk assessment was finally obtained by compiling the HQs of the four LOEs
into a single index (WOE index) associated with a global hazard class. In addition to
the quality and the relevance of the data, there are some prerequisites for parameter
integration in the model: the availability of a reference value for each endpoint and,
for biological endpoints, an additional threshold value defining the basal/natural
variations of the response considered is needed. Accordingly, around 160 endpoints
acquired between 2011 and 2012 were selected to be injected into the model. They
included 27 and 60 substances of concern for the water column and sediment
contamination, respectively (LOE chemistry); 37 compounds bioaccumulated in
gammarids (LOE bioavailability); 9 biological responses characterising neurotoxicity, energy acquisition, feeding rate, reproduction and survival in caged gammarids
(LOE biomarkers); and 11 and 14 endpoints assessing survival, development,
teratogenicity, growth, endocrine disruption, cytotoxicity and genotoxicity using
bioassays on water and sediment samples, respectively (LOE bioassays) [20]. Data
integration was performed for the three sites and the four sampling campaigns, as
well as for an annual average for each site. One of the strengths of the model stems
from the differential weighting of each endpoint. For instance, each compound
integrated into the chemical and the bioavailability LOEs is weighted according to
its status in the Water Framework Directive [63], giving higher weighting factors to
priority hazardous substances and priority substances. In the biomarker and bioassay
LOEs, each endpoint is weighted against the biological significance of the response
considered according to an arbitrary scale of 0–3. For bioassays, the weighting
factors also take into account the test matrix and the exposure duration [20, 62].
Moreover, the procedure was improved (1) using external reference values for
biomarkers and bioaccumulation levels established for the same population of
gammarids during previous studies and (2) integrating natural variations of the
responses as well as the effects of confounding factors.
4.3 Application of the Integrative WOE Approach to a 1-Year
Case Study on the Seine River
The HQs generated for the annual average clearly reflected the well-known anthropogenic gradient along the Seine River, with the lowest values observed for
260
M. Bonnard et al.
Disturbance
The WOE methodology consisted in gathering the selected parameters into four
LOEs: sediment and water chemistry (contamination level analysis), contaminant
bioavailability (bioaccumulation levels in caged gammarids), biomarker responses
(in gammarids) and bioassay responses (on sediment and water samples). A hazard
quotient (HQ) was then calculated for each LOE and reported in an evaluation grid
for a rapid and clear hazard classification (i.e. ranging from absent to severe). An
overall risk assessment was finally obtained by compiling the HQs of the four LOEs
into a single index (WOE index) associated with a global hazard class. In addition to
the quality and the relevance of the data, there are some prerequisites for parameter
integration in the model: the availability of a reference value for each endpoint and,
for biological endpoints, an additional threshold value defining the basal/natural
variations of the response considered is needed. Accordingly, around 160 endpoints
acquired between 2011 and 2012 were selected to be injected into the model. They
included 27 and 60 substances of concern for the water column and sediment
contamination, respectively (LOE chemistry); 37 compounds bioaccumulated in
gammarids (LOE bioavailability); 9 biological responses characterising neurotoxicity, energy acquisition, feeding rate, reproduction and survival in caged gammarids
(LOE biomarkers); and 11 and 14 endpoints assessing survival, development,
teratogenicity, growth, endocrine disruption, cytotoxicity and genotoxicity using
bioassays on water and sediment samples, respectively (LOE bioassays) [20]. Data
integration was performed for the three sites and the four sampling campaigns, as
well as for an annual average for each site. One of the strengths of the model stems
from the differential weighting of each endpoint. For instance, each compound
integrated into the chemical and the bioavailability LOEs is weighted according to
its status in the Water Framework Directive [63], giving higher weighting factors to
priority hazardous substances and priority substances. In the biomarker and bioassay
LOEs, each endpoint is weighted against the biological significance of the response
considered according to an arbitrary scale of 0–3. For bioassays, the weighting
factors also take into account the test matrix and the exposure duration [20, 62].
Moreover, the procedure was improved (1) using external reference values for
biomarkers and bioaccumulation levels established for the same population of
gammarids during previous studies and (2) integrating natural variations of the
responses as well as the effects of confounding factors.
4.3 Application of the Integrative WOE Approach to a 1-Year
Case Study on the Seine River
The HQs generated for the annual average clearly reflected the well-known anthropogenic gradient along the Seine River, with the lowest values observed for
260
M. Bonnard et al.