Example PNEC Derivation for a Realistic Worst Case Sediment

DATA COMPILATION AND DATA SCREENING

The quality screening criteria as defined in Data Quality Screening were applied to select the high quality chronic ecotoxicity data of nickel to freshwater sediment organisms. In total ecotoxicity data were available for 10 species. Two of the species produced unbounded values. An overview of all accepted individual high quality chronic ecotoxicity data is presented in Vangheluwe & Nguyen (2015) and Besser et al. (2013) and Table 1. In this example, the data were normalized towards the RWC physico-chemical conditions prevailing in sediments using the bioavailability models described in the Fact Sheet 9, Incorporation of Bioavailability in the Sediment Compartment. The RWC bioavailability is characterized by a low AVS content (i.e. 0.8 µmol AVS/g dry wt.).

Table 1: Selected freshwater sediment normalized species mean ecotoxicity data
to nickel for the most sensitive endpoint (Vangheluwe & Nguyen, 2015) 

Taxonomic Group

Species

Life History/

Feeding Strategy

Most Sensitive Endpoint

Normalized Species Mean (NOEC/L(E)C10 Value

(mg Ni/kg dry wt.)

Crustaceans

Hyalella azteca

Gammarus pseudolimnaeus

Swimmer, sprawler,

surface deposit feeder

Biomass

Biomass

203.5

348.4

Insects

Ephoron virgo

Hexagenia sp.

Chironomus riparius

Chironomus dilutus

Burrower, surface and subsurface feeder

Biomass

Biomass

Development

141.1

188.7

673.5

*

Oligochaetes

Lumbriculus variegatus

Tubifex

Burrower, subsurface feeder

Abundance

Biomass

529.8

1000.3

Mollus

Sphaerium corneum

Lampsilis siliquoidea

Burrower, surface

deposit feeder

Biomass

322.1

*

*   Unbounded value >762 mg Ni/kg dry wt.

 

DATA AGGREGATION AND OVERVIEW NICKEL SEDIMENT ECOTOXICITY DATABASE

The normalized chronic data from each test on a given sediment species were aggregated according to the criteria mentioned in Data Aggregation. An overview of the normalized species mean L(E)C10 value for the most sensitive endpoint is provided in Table 1.

SSD CONSTRUCTION AND MEDIAN HC5 DERIVATION

The normalized species mean NOEC/L(E)C10 values in Table 2 were ranked from low to high. Subsequently, a log-normal distribution was fitted through the ranked species means . The median HC5 value calculated for the for RWC ecotoxicity data was 109 mg Ni/kg dry wt. (Figure 4).

Table 2: Overview of the water chemistry and median HC5/PNEC values
for the different selected EU eco-regions (values between brackets are 90% confidence intervals)

Eco-Region

Sediment Chemistry

(µmol AVS/g dry wt.)

Median HC5

(mg nickel kg dry wt.)

PNEC

(mg nickel kg dry wt.)2

Generic Reasonable Worst Case Sediment

0.8

109 (40-182)

109

Spring River, Missouri, USA

0.9

115 (43-191)

115

Dow Creek, Michigan, USA

1.0

121 (46-201)

121

Brakel 1, Belgium

2.6

165 (66-264)

165

St. Joseph River, Michigan, USA

3.8

185 (75-296)

185

Raisin River (site 2), Michigan, USA

6.1

210 (85-337)

210

Brakel 2, Belgium

6.2

212 (86-339)

212

Raisin River (site 3), Michigan, USA

8.0

225 (91-336)

225

USGS Survey Pond 30, Missouri, USA

12.4

249 (99-403)

249

Lampernisse, Belgium

24.5

284 (108-469)

284

South Tributary Mill Creek, Michigan, USA

24.7

284 (108-470)

284

West Bearskin Lake, Minnesota, USA

38.4

305 (111-515)

305

 2  PNEC is calculated using an AF of 1

 

Figure 4: SSD and median HC5 derivation for nickel using normalized
ecotoxicity data for a RWC sediment containing 0.8 µmol AVS/g dry wt.

Figure 4

PNEC DERIVATION

When an AF of 1 is used, the PNEC value is equivalent to the HC5.  Therefore, the RWC PNEC is 109 mg Ni/kg dry wt.

The example of the SSD construction and PNEC derivation for nickel presented here applies for RWC sediment chemistry (i.e., low in AVS). However, a range of AVS concentrations can be encountered in the EU, which results in different PNEC values. Several bioavailability scenarios encompassing the range of AVS typically encountered in sediments (1-40 µmol/g dry wt.) are shown in Table 2. The AVS concentrations and HC5-50/PNEC values (AF = 1) calculated for the different selected freshwater sediments are summarized in Table 2.

When the range of AVS values observed in natural sediments is taken into account, PNEC values range from 109 mg Ni/kg dry wt. for the RWC scenario to 305 mg Ni/kg dry wt. for the high end of the AVS distribution (Table 2).