Sodium nitrate

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:

comparable to guideline study with acceptable restrictions

Qualifier:

no guideline followed

Principles of method if other than guideline:

Ten cultures of benthic diatoms were isolated from field samples from Eems Dollard Estuary (The Netherlands). The growth rate was determined as % chlorophyll a in diatoms grown in an artificial sea water medium containing increasing amounts of potassium nitrate. The test substance concentration was controlled using an auto-analyzer. The salinity of the test medium was kept constant at 15 or 37% depending on the algal strain tested. The climate room was maintained at 12ºC, with a quantum irradiance of 85 NE.m-2.sec-1 (4000 lux) from extra cool-white fluorescent tubes and a light period of 16 hours/day. In addition, the pH of the medium increased with a maximum of 0.4 after 24 hours incubation, most likely due to photosynthesis.

GLP compliance:

no

Analytical monitoring:

yes

Vehicle:

no

Test organisms (species):

other: several benthic diatoms; see results

Details on test organisms:

TEST ORGANISM
- Strain: benthic diatoms
- Source (laboratory, culture collection): isolated from field samples from Eems Dollard Estuary (The Netherlands).

Test type:

static

Water media type:

saltwater

Limit test:

no

Total exposure duration:

10 d

Test temperature:

The climate room was maintained at 12ºC.

Salinity:

The salinity of the test medium was kept constant at 15 or 37% depending on the algal strain tested.

Nominal and measured concentrations:

Nominal nitrate concentrations: 0.1, 0.68, 3.38, 6.75 and 16.9 mmol/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 100 mL Erlenmeyers with a thin layer of analytical clean sand
- Material, size, headspace, fill volume: 40 mL
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Artificial seawater, prepared according to Provasoli et al (1957), medium U

0.2 g/L NaHCO3
0.5 g/L tris buffer pH 8.0)
"minor elements"
26 mg/L HBO4
Vitamins, silicates and trace elements were added as in "f" medium described by Guillard and Ryther (1962)

OTHER TEST CONDITIONS
- Adjustment of pH: the pH of the medium increased with a maximum of 0.4 after 24 hours incubation, most likely due to photosynthesis.
- Photoperiod: quantum irradiance of 85 NE.m-2.sec-1 (4000 lux) from extra cool-white fluorescent tubes and a light period of 16 hours/day.
- Salinity (for marine algae): The salinity of the test medium was kept constant at 15 or 37% depending on the algal strain tested.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Chlorophyll measurement: the growth rate was determined as % chlorophyll a

Key result

Duration:

10 d

Dose descriptor:

EC50

Effect conc.:

> 1 700 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Most of the species (8 out of 10 tested, e.g. Navicula arenaria, Nitzschia dubiformis etc.) grew well at nitrate concentrations up to 16.9 mmol/L (=1.7 g/L). Nitrate was only clearly inhibitory to Nitzschia dubiformis and Amphiprora c.f. paludosa only at the highest test concentration.

Relative rates (as % chlorophyll a) were:

                                                           Nitrate concentration (mmol/L)

           Species                                    0.1       0.68     3.38     6.75     16.9     

           Navicula arenaria                  80        95        100      107      94

           Nitzschia c.f. dissipata            84        94        100      83        67

           Nitzschia dubiformis               67        84        100      100      34

           Nitzschia closterium                54        65        65        85        100

           Amphiprora c.f. paludosa       71        89        86        100      39

           Stauroneis constricta              52        92        98        102      100

           Navicula cryptocephala          61        82        73        100      84

           Navicula salinarum                 65        73        89        100      86

           Gyrosigma spencerii               76        100      100      91        70

           Nitzschia sigma                       92        75        100      98        58

Validity criteria fulfilled:

not applicable

Conclusions:

Most of the species grew well at nitrate concentrations up to 16.9 mmol/L (=1.7 g/L). Nitrate was clearly inhibitory to Nitzschia dubiformis and Amphiprora c.f. paludosa only at the highest test concentration.

Description of key information

No reliable study with sodium nitrate is available. Based on a reliable study with potassium nitrate, it was shown that the substance was not at all or only slightly inhibitory at the highest concentration tested (10 different algae tested).

Key value for chemical safety assessment

EC50 for freshwater algae:

1 700 mg/L

EC10 or NOEC for freshwater algae:

1 700 mg/L

Additional information

No reliable study with sodium nitrate is available. A reliable study with ten cultures of benthic diatoms was performed with potassium nitrate. Diatoms were isolated from field samples from Eems Dollard Estuary (The Netherlands). The growth rate was determined as % chlorophyll a in diatoms grown in an artificial sea water medium containing increasing amounts of potassium nitrate. The test substance concentration was controlled using an auto-analyzer. The salinity of the test medium was kept constant at 15 or 37% depending on the algal strain tested. The climate room was maintained at 12ºC, with a quantum irradiance of 85 NE.m-2.sec-1 (4000 lux) from extra cool-white fluorescent tubes and a light period of 16 hours/day. In addition, the pH of the medium increased with a maximum of 0.4 after 24 hours incubation, most likely due to photosynthesis. Most of the species (8 out of 10 tested, e.g. Navicula arenaria, Nitzschia dubiformis etc.) grew well at nitrate concentrations up to 16.9 mmol/L (=1.7 g/L). Nitrate was only clearly inhibitory to Nitzschia dubiformis and Amphiprora c.f. paludosa only at the highest test concentration.