Table 1.

Examples of the use of Species Sensitivity Distributions in several regulatory frameworks for the purposes of chemical risk assessment and formulation of water quality criteria or standards. The table is non-exhaustive and other frameworks are used by hazard assessors globally.

		Standard for Acceptance in Regulatory Framework
Facet of SSD Development	Factors to be considered	ECHA 2008	USEPA Ambient Water Quality Criteria, Stephan et al. 1985	CCME 2013	ANZECC and ARMCANZ (2000) supplemented by Warne et al. (2015)
Type of regulatory use		Chemical hazard assessment under REACH	Development of chemical discharge criteria and impaired water assessments	Development of chemical discharge criteria, also used in chemical hazard assessment	Development of chemical discharge criteria
Overall quality of the database	Information or data source	Klimisch scoring, preferably in IUCLID5, documented	Data available in typed and dated form (publication, manuscript, letter, memorandum, etc.); supporting information indicates acceptability results are probably reliable	Use of acceptable laboratory practices in design and execution of tests. Each study is classified as primary, secondary, or unacceptable, based on detailed inclusion criteria.	Scored using a reliability assessment system specific to Australia and New Zealand
	Are data generated from true chronic studies	Required	Acute data required; chronic data are needed for Acute:chronic ratio (ACR) determination	Required for primary data	Required for chronic SSD formulation; note that acute SSDs can be generated as well
	Chronic studies cover sensitive life stages	Required	Not required	Required for primary data	Not defined; notation of life stages is required
	Endpoints used as input are the lowest NOECs or ECx values of the endpoints measured in relevant studies	Required	EC50 and LC50 data required; NOEC/LOEC data are needed for ACR determinations	ECx prefered over NOECs (× 10 or less)	ECx is preferred over NOECs from all studies and endpoints on each species
	Treatment of endpoint data for multiple tests on same species	Not specified	Always uses survival or immobility endpoints thus records are similar by definition; LC50 and EC50 estimates calculated at the genus level as geometric means	Median value for comparable records for the same endpoint when more than two data points are available; if only two the geometric mean is used to represent the average species effects endpoint	Data for each species and endpoint expressed as a geometric mean and the lowest value per species is used
	Use of Data on Most Sensitive Endpoints	NOEC conclusions from the quoted studies should represent the most sensitive endpoint for the test	See above	See above	See above
Taxonomic Groups Considered	Fish	At least two species	Salmonid is required; second species of commercial or recrational importance is recommended (a second fish is required)	Three species including one coldwater species (salmonid), one warmwater species, and one other.	No specific organism types are required; at least 4 phyla needed
	Additional vertebrates	Not required	Third chordate family required (amphibian or third family of fish)	Amphibian highly desired, but not required	Not specified
	Crustaceans	At least one species	Required	Required	Not specified
	Insect	At least one species	At least one species	Mayfly, stonefly or caddisfly preferred but not required	Not specified
	Additional invertebrates	At least one additional phylum not represented by Insects or Crustaceans	At least one more family in a phylum other than Arthropoda or Chordata and at least one more family in any order of insect or any phylum not already represented	Two additional invertebrates required	Not specified invertebrates
	Algae (number unspecified)	Required but number unspecified	Not used	One species of a plant or alga is required; three required if indications exist that photosynthetic organisms are sensitive	Not specified
	Higher plants (number unspecified)	Required but number unspecified	Not used	One species of a plant or alga is required; three required if indications exist that photosynthetic organisms are sensitive	Not specified
Minimal Sample Size	Total number of species in SSD	10 NOECs, preferably more than 15 for different species	8 different families required	At least 10, preferably 15 different species	Minimum of 5 species from at least 4 taxonomic groups, preferably more than 5 species
Statistical Fit to A Distribution	Use of Underlying Distribution	Confirm model choice, flexible for data, but lognormal and log logistic identified as most common	Log triangular required applied to the four most sensitive genera	Confirm model choice	Burr Type III distribution recommended (note this includes log-normal, log-logostic and log-triangular)
	Statistical Goodness of Fit	Confirm by appropriate GoF test	Not considered	Confirm GoF	Confirm GoF
	Conclusion	Provided overall statement as fit for purpose	Generally should discuss	Generally should discuss	Generally should discuss
Estimated Parameter	HC5 and Confidence interval	HC5 with 50% CI derived and provided	HC5 is derived as input into further calculations to establish the water quality criterion	HC5 with 95% CI derived and provided	HC1, HC5, HC10 and HC20 with 50% CI derived and provided to address various protection targets
NOEC values below the HC5	Discuss values that fall below the HC5	Required	If economically or recreationally important species fall below the HC5, the criterion will be lowered to protect those species.; although algae and plants are not included in the SSD, algae and plant toxicity data are compared to the HC5	Discuss	HC5 should be less than the chronic effect concentration for high value or keystone species
Distribution of trophic levels within the SSD	Discuss trophic level influences	Assess distribution of trophic level within the chosen distribution; use multiple curves if bi- or multi-modal	Not required	Assess distribution of trophic level within the chosen distribution; use multiple curves if bi- or multi-modal	Assess distribution of trophic level within the chosen distribution; use multiple curves if bi- or multi-modal
Knowledge of the Mode of Action	Discuss	Required	Indicated in documentation	Required	Indicated in documentation