Reaction products of sodium glucoheptonate with zinc sulfate and sodium hydroxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge nitrification inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2003

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

equivalent or similar to guideline

Guideline:

ISO 9509 (Toxicity test for assessing the inhibition of nitrification of activated sludge microorganisms)

Deviations:

not specified

GLP compliance:

not specified

Test organisms (species):

activated sludge, domestic

Test type:

other: isothermal, closed and well-mixed reactor equipped with a Dissolved Oxy-|fen probe, temperature gauge. pH controller, magnetic Stirrer, and porous aerator.

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20°C

pH:

6.5 - 7.5

Dissolved oxygen:

5 - 6 mg/L

Nominal and measured concentrations:

0.3 - 1.2 mg/L

Details on test conditions:

The experiments were performed in two isothermal, closed and well-mixed reactors, one as a reference of the noninhibited system, and one with the inhibitor to be tested. Each reactor was filled with 400 mL of activated sludge collected from a municipal wastewater treatment plant at 3-3.5 g/L MLSS, 80 mL of substrate fluid [solution of NaHCO3, and (NH4)2SO4), 20 mL of basic-standard food (solution of (NH4)2HPO4, NaCl, CaCl2-2H2O, MgSO4-7H2O and FeCl3-6H2O) and either 400 mL of distilled water (reference) or of the sample to be tested, possibly diluted to 400 mL with distilled water (test reactor). The concentrations of nitrite and nitrate were first measured at t = 0 h by a spectrophotometer. These concentrations were again measured after set times. This experiment took place at a constant temperature of 20°C. The reactor was equipped with a Dissolved Oxygen probe, temperature gauge, pH controller, magnetic Stirrer, and porous aerator. The experiment was carried lout at a pH of 6.5-7.5. The level of dissolved oxygenwas kept between 5 and 6 mg/L by periodically aerating jhe activated sludge mixture.

Reference substance (positive control):

no

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

0.35 mg/L

Nominal / measured:

not specified

Conc. based on:

element

Basis for effect:

inhibition of nitrification rate

Duration:

3 h

Dose descriptor:

other: IC20

Effect conc.:

0.16 mg/L

Nominal / measured:

not specified

Conc. based on:

element

Basis for effect:

inhibition of nitrification rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

0.1 mg/L

Nominal / measured:

not specified

Conc. based on:

element

Basis for effect:

inhibition of nitrification rate

Details on results:

The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. The influence of the heavy metals concentration on the production of nitrite and nitrate is given as % inhibition. Consequently, the % inhibition increases as the concentration of heavy metals increases. For example. 97% inhibition of nitrification is reached at 1.2 mg/L Zn2+. The nitrite and nitrate production were affected to a lesser degree at Zn2+ = 0.3 mg/L; the value of the % inhibition is 37% at this concentration. The IC20 is reached at 0.16 mg/L Zn2+. The nitrite and nitrate production are reduced by Zn2+ at concentrations above 0.3 mg/L. The IC50 is reached at 0.35 mg/L Zn2+.

Conclusions:

The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. Consequently, the % inhibition increases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L, the IC20 is reached at 0.16 mg/L Zn2+ and the IC50 is reached at 0.35 mg/L Zn2+.

Executive summary:

In this study the ISO 9509 test was used to assess the inhibitory effect of Zn2+ on nitrification of municipal wastewater samples using activated sludge collected from a municipal wastewater treatment plant. The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L, the IC20 is reached at 0.16 mg/L Zn2+ and the IC50 is reached at 0.35 mg/L Zn2+.

Description of key information

There is no data available for the target substance zinc glucoheptonate on toxicity towards microorganisms. However, there is data available for the read-across substances zinc sulphate. This data is used within a frame of a weight-of-evidence approach to assess the toxicity of zinc glucoheptonate.

Dalzell et al., 2002

Five rapid direct toxicity assessment methods were used to determine the toxicity of single toxicants, mixed toxicants and real industrial wastes. Nitrification inhibition, Respirometry, Adenosine triphosphate luminescence and Enzyme inhibition were tested utilising activated sludge as the testing matrix. TheVibrio fischeritoxicity test was used as a surrogate to compare the various microbial bioassays.

It was shown that IC50 values for Zn using the five different assays measuring different endpoints ranged between 0.8 and 80 mg/L. In the standardV. fischeriassay (microtox bioassay), the IC50 for Zn was the lowest with around 0.8 mg Zn/L (5.05 mg ZnGHA/L). The Enzyme and respiratory inhibition had similar results. The IC50 were at about 80 mg/L (504.95 mg ZnGHA/L), whereas the IC50 for the nitrification inhibition was at 10 mg/L (63.12 mg ZnGHA/L).

Dutka et al., 1983

Four short-term microbiological toxicity screening tests were compared using the following test chemicals: 3,5 dichlorophenol, cetyl trimethyl ammonium chloride, sodium lauryl sulfate, phenol, copper(II) sulfate, mercury(II) chloride and zinc(II) sulfate. These seven chemicals represent a wide range of toxicity. The methods examined were Beckman's Microtox system, theSpirillum volutansmotility test, inhibition of respiratory activity of activated sludge, and inhibition of activated sludge TTC-dehydrogenase activity. The results obtained indicate that each method has its own toxicity sensitivity pattern. With the Microtox assay EC50 values determined for Zinc are 13.8, 6.1 and 3.45 mg/L (87.1, 38.5, 21.78 mg ZnGHA/L) for an exposure time of 5, 10 and 15 min. TheSpirillum volutansassay revealed an IC90 value for zinc of 11.6 mg/L (73.22 mg ZnGHA/L). In the respiratory activity test EC50 values of 6.1 and 5.2 mg/L (38.5 and 32.82 mg ZnGHA/L) were measured after an exposure time of 0.5 and 3 h, respectively. The TTC dehydrogenase test revealed an EC50 value of 24 mg/L (151.49 mg ZnGHA/L).

Juliastuti et al., 2003

In this study the ISO 9509 test was used to assess the inhibitory effect of Zn2+ on nitrification of municipal wastewater samples using activated sludge collected from a municipal wastewater treatment plant. The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L (0.63 mg ZnGHA/L), the IC20 is reached at 0.16 mg Zn /L (1.01 mg ZnGHA/L) and the IC50 is reached at 0.35 mg Zn /L (2.21 mg ZnGHA/L).

Conclusion

The EC50-values for ZnGHA on microorganisms range between 2.21 and 504.95 mg ZnGHA/L. The maximum, as well as the minimum value were derived using activated sludge. This shows that there is a great variation between the different methods.

Table 1: Effect concentration (EC)-values from studies performed with elemental zinc (Zn2+) converted to ZnGHA under consideration of the purity

Species/ activated sludge	Duration of exposure	Dose descriptor	Basis for effect	elemental Zn in source substance [mg/L]	ZnGHA (75%) [mg/L]	Reference
activated sludge	2 h	IC50	inhibition of nitrification	10	63.12	Dalzell et al. 2002
	3h	IC50	inhibition of respiration	80	504.95
	15 min	IC50	inhibition of enzyme activity	80	504.95
V. fischeri	15 min	IC50	inhibition of respiration	0.8	5.05
activated sludge (microtox assay)	5 min	EC50	alteration of metabolism	13.8	87.10	Dutka et al. 1983
activated sludge (microtox assay)	10 min	EC50	alteration of metabolism	6.1	38.50
activated sludge (microtox assay)	15 min	EC50	alteration of metabolism	3.45	21.78
Spirillum volutans	2 h	IC90	elimination of reversing motility	11.6	73.22
activated sludge (respiratory activity test)	0.5 h	EC50	respiratory activity	6.1	38.50
activated sludge (respiratory activity test)	3 h	EC50	respiratory activity	5.2	32.82
activated sludge (TTC dehydrogenase test)	1 h	EC50	Inhibition of dehydrogenase	24	151.49
activated sludge	3 h	IC50	nitrification inhibition	0.35	2.21	Juliastuti et al. 2003
activated sludge	3 h	IC20	nitrification inhibition	0.16	1.01
activated sludge	3 h	NOEC	nitrification inhibition	0.1	0.63

Key value for chemical safety assessment

EC50 for microorganisms:

2.21 mg/L

EC10 or NOEC for microorganisms:

0.63 mg/L