EFSA: Scientific Opinion on the effect assessment for pesticides on sediment organisms in edge-of-field surface water

The EFSA Panel on Plant Protection Products and their Residues (PPR Panel) has published the second of three requested deliverables within  his mandate to revise the Guidance Document (GD) on Aquatic Ecotoxicology under Council Directive 91/414/EEC (SANCO/3268/2001 rev. 4 (final), 17 October 2002). Further to the publication in July 2013 of the Guidance Document on tiered risk assessment for aquatic organisms in edge-of-field surface waters (EFSA Journal 2013;11(7):3290) , this new scientific opinion deals with the effect assessment for sediment organisms (EFSA Journal 2015;13(7):4176) and in particular with:

• the benthic ecology of edge-of-field surface water

  • physical, chemical and biological diversity of sediment habitats;

  • benthic communities (microorganisms, microphytobenthos, rooted macrophytes, meiobenthos such as nematodes and macrobenthos such as larvae of insects, macro-crustaceans…);

  • exposure routes (via contact, food).

• the identification of standard test species and standardised test systems

  • internationally accepted protocols on a limited number of taxa (insects with Chironomus spp., crustacean with Hyalella azteca, oligochaete with Lumbriculus variegatus and rooted macrophyte with Myriophyllum spp.): development needed;

  • differences between OECD and US EPA protocols (nature of sediment, spiking procedure): need for comparative studies to identify consequences on toxicity estimates.

• the identification of specific protection goals (SPGs)

  • ecological threshold option (ETO) considered as the best option to provide adequate protection of benthic organisms, in comparison to  ecological recovery option (ERO).

• the proposition of trigger for sediment testing

  • (1) if more than 10 % of the radio-labelled test material found in the sediment at or 14 days after application in the standard water–sediment fate study (OECD Guideline 308), or more than 10 % of the total annual dose of the active substance in sediment at the time of maximum PECsed as assessed by FOCUS modelling;

  • and (2) if the chronic NOEC/EC₁₀ of Daphnia or another relevant pelagic animal species is less than 0.1 mg/L, or the EC₅₀ of the standard test alga or vascular plant is less than 0.1 mg/L.

• the definition of regulatory acceptable concentrations (RACs)

  • RACs expressed in terms of (1) total sediment concentration (dry weight) normalised to either the OC content in the dry sediment or to standard OECD sediment with an OC content of 5 %, and of (2) the freely dissolved fraction in pore water;

  • use of the 0–1 cm sediment layer for PECsed derivation for benthic fauna and microorganisms;

  • use of the 0–5 cm sediment layer for rooted macrophytes;

  • RACs derivation based on chronic toxicity data using sediment-spiked tests and benthic organisms (NB: semi-chronic toxicity data can also be used with an appropriate additional extrapolation factor).

• the use of  a tiered approach for the exposure assessment

  • FOCUS methodology in 4 steps;

  • proposal for the inclusion of an accumulation factor to account for the effect of multi-year applications, not considered in the current FOCUS approach;

  • need for new sediment scenarios for total content and pore water concentrations to improve FOCUS assessment.

• the use of a tiered approach for the effect assessment

  • a screening step based on chronic toxicity data for pelagic organisms and the equilibrium partitioning (EqP) approach, with an extrapolation factor of 10 for benthic fauna to cover the possibility of exposure due to sediment ingestion;

  • a first tier based on chronic standard tests with a decision scheme to select the appropriate benthic test species;

  • a second tier based (1) on chronic standard tests on additional test species with the use of the Weight of Evidence (WoE) approach (geomean approach not advised), and (2) on the use of Species Sensitivity Distribution (SSD) approach if sufficient number of benthic species (at least 8 species of the potentially sensitive taxonomic group (most likely benthic arthropods for insecticides; rooted macrophytes for herbicides), or 8 toxicity data for at least 5 different taxonomic/feeding groups if no specific potential sensitive taxonomic identified);

  • a third tier based on micro/mesocosms studies using preferably field-collected sediment and combined exposure routes (both water and sediment spiking), monitoring of exposure concentrations, observations of long-term benthic population and community-level effects;

  • To be highlighted: no consolidated ERA scheme available at this stage; need for more research and analysis of data to identify the most relevant exposure routes, depending on aquatic vertebrate species and substances.

• the risk characterisation for active substances of PPP and their metabolites (ratio between effects and  exposure levels)

  • RACsed expressed in terms of initial exposure concentrations vs. PECsed, max as realistic worst-case;

  • PECsed, twa only used when field exposure concentrations being sufficiently variable during a time frame smaller than the duration of the sediment-spiked toxicity test that drives the RACsed;

  • two senarios advised: one with low OC (worst-case pore water scenario) and one with high OC (worst-case total content scenario);

  • need for the development of  environmental scenarios for ponds, ditches and streams;

  • relative contribution of the older (e.g. > 1 year) and recent fractions (e.g. latest growing season) in the PECsed,tot to be considered in a higher tier.

A later PPR Panel scientific opinion will deal with possible mechanistic effect models that can be used in the aquatic risk assessment for sediment-dwelling organisms. The adoption is foreseen for end 2017.