Chlorpyrifos

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Batch Number: RMM 1430
Purity: 96.4%

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 0.0625, 0.125, 0.25, 0.5, 1.0 mg/L
- Sampling method: The contents of the bottles were transferred to separating funnels containing NaCl (4 g) and the bottles rinsed with dichloromethane (50 ml) which was also transferred to the separating funnel. The layers were shaken (1 minute) then following separation, the lower organic layer was drained into a round bottom flask. The aqueous layer was re-extracted with dichloromethane (50 ml) and the organic layers combined. The solvent was evaporated just to dryness (rotary film evaporator, 30°C) and any remaining solvent removed under nitrogen. The extracts were dissolved in 2,2,4-trimethylpentane and analysed by Gas Liquid Chromatography against standards prepared from test substance.
- Sample storage conditions before analysis: Frozen

Vehicle:

yes

Remarks:

1% Tween 80 acetone

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Preliminary solution in 1% Tween 80 acetone
- Controls: 1 control and 1 solvent control
- Chemical name of vehicle: Organic solvent (1% Tween 80 acetone)

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Green Algae - Chlorophytes
- Strain No.: CCAP 276/20
- Source (laboratory, culture collection): Culture Centre of Algae & Protozoa c/o Freshwater Biological Association, Cumbria, U.K.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Test temperature:

24 ± 1°C

pH:

~8

Nominal and measured concentrations:

62.5, 125, 250, 500, 1000 µg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mL conical flasks
- Type: Closed
- Aeration: None. Gaseous exchange and suspension of algal cells maintained by orbital shaker.
- Initial cells density: The cell densities of the control cultures at initiation, 72 hours and at termination were determined by direct counting with the aid of a haemacytometer.
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): 3

GROWTH MEDIUM
- Standard medium used: Yes (nutrient medium)

OTHER TEST CONDITIONS
- Sterile test conditions: Yes
- Photoperiod: Continuous
- Light intensity: ~7000 lux

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

580 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: Nominal effect conc.: 800 µg/L

Key result

Duration:

96 h

Dose descriptor:

EC50

Effect conc.:

480 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: Nominal effect conc.: 660 µg/L

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 730 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: Nominal effect conc. (24-48 h): >1000 µg/L (highest dose tested)

Key result

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

43 µg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Remarks on result:

other: Nominal effect conc.: 62.5 µg/L

Details on results:

- Observation of abnormalities: All test and control cultures were inspected at 72 and 96 hours. At both these periods during the study, clumping was apparent at 500 and 1000 µg/L. No abnormalities were detected in any of the other cultures.
- The inhibitory effects on growth occurred predominantly after 48 hours exposure, hence the apparent anomaly between the ErC50 (24 - 48 h) and EbC50 (72 hand 96 h) values.
- Care should be exercised in the interpretation of these results since it was observed that exposure levels could not be maintained at near nominal values throughout the study. Mean measured concentrations were 73% of nominal at the start of the test and 6-20% of nominal at the end (mean value 14%). Adsorption may have accounted for some of the apparent losses but assimilation by the algae may have been a contributing factor, especially at 96 hours.

Validity criteria fulfilled:

yes

Conclusions:

72 h EbC50 (green algae): 580 µg/L
96 h EbC50 (green algae): 480 µg/L
24-48 h ErC50 (green algae) >730 µg/L (highest dose tested)
NOEC (green algae): 43 µg/L

Executive summary:

A study was performed to assess the inhibitory effect of the test substance on the growth of the unicellular green alga Scenedesmus subspicatus (Chodat). The study was conducted in accordance with OECD Guideline No. 201 with an exposure period of 96 hours.

Algal cultures exposed to five concentrations of test substance plus one untreated control and one solvent control were incubated on an orbital shaker under continuous illumination at 24 ± 1°C for 96 hours. Growth was monitored daily by measuring the absorbance of the cultures at 665 nm.

The following values were derived form the data, based on nominal concentrations:

EbC50 (72 h): 800 µg/L

EbC50 (96 h): 660 µg/L

ErC50 (24-48 h): >1000 µg/L

NOEC: 62.5 µg/L

Mean measured concentrations were 73% of nominal at the start ofthe test and 14% at the end. Consequently, results are also expressed in terms of initial measured concentration:

EbC50 (72 h): 580 µg/L

EbC50 (96 h): 480 µg/L

ErC50 (24-48 h): >730 µg/L

NOEC: 43 µg/L

Description of key information

72 h EbC50 (green algae, Desmodesmus subspicatus): 580 µg/L, 96 h EbC50 (green algae): 480 µg/L; OECD 201; Reliability = 2

Key value for chemical safety assessment

EC50 for freshwater algae:

480 µg/L

EC10 or NOEC for freshwater algae:

43 µg/L