Sodium sulphate

Toxicity to terrestrial plants

Administrative data

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Literature data.

Data source

Reference

Reference Type:

publication

Title:

Toxicity and accumulation of chloride and sulfate salts in plants

Author:

Eaton Frank M.

Year:

1942

Bibliographic source:

Journal of Agricultural Research, Washington, D. C.Vol. 64 No. 7 April 1, 1942 Key No. G-1248

Materials and methods

Principles of method if other than guideline:

Effect of sulfate salt on a series of crop plants in outdoor sand cultures. A series of crop plants was grown to maturity in each of six large outdoor sand cultures supplied with a base nutrient and with sulfate salt (50 percent as sodium) added, in milliequivalents per liter, as follows: Control, 50-sulfate, 150- sulfate and 250-sulfate. Physical and chemical properties of plant sap were then evaluated.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Sulphate salt

IUPAC Name:

Sulphate salt

Test substrate

Details on preparation and application of test substrate:

The treatments consisted of a control bed supplied with a base nutrient solution, which was the same in all the cultures, three sulfate beds in which concentrations of 50, 150 and 250 milliequivalents, respectively, of sulfate ion per liter were maintained. Fifty percent of the sulfate ions was added as sodium salts, with the remaining 50 percent divided between calcium and magnesium salts. In the 50-sulfate bed magnesium sulfate was substituted for calcium sulfate above 20 milliequivalents per liter in the 150- and 250-sulfate beds.
Tap water was used in the preparation and replenishment of the culture solutions.

Test organisms

1

Species:

Sorghum vulgare

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Dwarf milo

2

Species:

other: Gossypium hirsutum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Acala cotton

3

Species:

other: Citrus limonia Osbeck

Details on test organisms:

- Common name: rooted lemon cuttings

4

Species:

Hordeum vulgare

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: barley

5

Species:

Phaseolus vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: navy beans

6

Species:

Beta vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: sugar beets

7

Species:

other: Medicago sativa

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: alfalfa

8

Species:

Lycopersicon esculentum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: tomatoes

Study design

Study type:

semi-field study

Substrate type:

natural soil

Test conditions

Details on test conditions:

TEST SYSTEM
- Reason for culture choice: the culture of a series of crop varieties together in sand beds or water cultures for a study of comparative physiology affords the best possible assurance that all are subjected to the same substrate conditions.
- Planting: the eight crops were planted in parallel 18-inch rows in each of the six sand beds.
- Solution administration: the plantings were carried beyond germination with the base nutrient solution plus one-fifth of the final quantity of the sulfate salt. Additional fifths of salt were added. A half portion of each of the solutions with the final concentration of salt was then made up, used to flush the sand and discarded.
- Soil properties: the nitrate concentrations in all solutions were measured periodically, and deficiencies from the initial concentrations were replaced by
additions of potassium nitrate or ammonium nitrate.
- Solution uptake: the solution held by the sand was replaced once each morning while the plantings were small, but as they became larger the operation was repeated a second time shortly after noon.

Extraction of plant sap.
- Samples: samples of freshly picked leaves, or entire tops in the case of alfalfa and barley were collected.
- Method of analysis: samples were compacted in glass tubes, which were then stoppered and scaled with paraffin paper secured in place with rubber bands. These tubes were packed in solid carbon dioxide and allowed to stand overnight, after which the samples were thawed out one at a time and the sap was expressed while still cold by the gradual application of pressure of 2400 pounds per square inch in a Carver press having monel-metal parts. The samples were left at this pressure for several minutes or until the rate of sap release became very slow.
- Sap analysis: each crop is considered in turn and the effect of the added salts is shown on the pH value, electrical conductance and ionic concentration. There was insufficient material for sap analyses of the lemons and navy beans and only partial analyses were made of the barley. The agricultural plants used for the salt-uptake comparisons represent five well differentiated botanical families, namely, the Gramineae (two representatives), the Leguminosae, the Malvaceae, the Solanaceae and the Chenopodiaceac.

EFFECTS RECORDED
Accumulation of salt costituents in plant sap.
Freezing-point depression on plant sap and differentials between sap and substrate.
Water requirements.
Plant injury in relation to salt accumulation.

Nominal and measured concentrations:

50, 150 and 250 milliequivalents sulfate ion per liter.

Results and discussion

Effect concentrations

Remarks on result:

not measured/tested

Any other information on results incl. tables

PLANTS ANALYSIS

TOLERANCE

- Lemon plants: two of the three rooted cuttings set out in the 250-sulfate bed lived until the end of the season, all of them making some growth.

- Milo: non-relevat effects observed.

- Alfalfa: three cuttings were made and there was considerable variation in the growth depression of these successive crops int he sulfate series.

- Cotton plants: the vegetative growth was reduced relatively more by sulfate salt than was the yield of seed cotton.

- Tomatoes: fruit production was depressed by salt roughly in proportion to the respective reductions in vine growth in the 50-sulfate beds, but in the beds maintained with higher salt concentrations blossom-end rot became the dominant factor in yield.

- Barley: the barley in the control bed was severely affected with mildew, but there was little or none on the plants in the salt beds. Because of the poor condition of the control barley, satisfactory conclusions cannot be drawn with respect to this plant’s salt tolerance. It may be noted, however, that the reductions in yield between the 50-, 150 - and 250-sulfate beds are proportionately much sharper than was the case with some other crops, indicating that mildew had substantially reduced the growth of the control plants.

- Sugar beets: showed a low degree of tolerance to sulfate salts; a greater reduction in yield was found to result from 50 milliequivalents.

Growth of plants in 100 and 200 milliequivalents of sulfate (average of 50 and 150 milliequivalents and 150 and 250 milliequivalents of sulfate) relative to the control plants

Crop	Sulfate
	100 milliequivalents	200 milliequivalents
Lemon cuttings	59%	24%
Navy beans (seed)	45%	/
Dwarf milo (grain)	60%	24%
Chilean alfalfa (3 cuttings)	75%	63%
Acala cotton (seed cotton)	77%	57%
Stone tomatoes (entire)	64%	40%
Sugar beets (fresh roots)	80%	71%

SYMPTOMS

- Lemon plants: the leaves of lemon plant’s in the control bed were larger than those in the salt beds and the control plants were more vigorous and healthy in appearance. Nevertheless, symptoms of diagnostic value were lacking except for some yellowing, which preceded leaf abscission in

the sulfate beds.

- Beans: the size of the leaves of the beans in the salt beds was reduced roughly in proportion to the reduction in plant size, but, the size of the mature seeds was not affected. When harvested the control plants and the plants in the 50-sulfate bed had a few dead leaves, but nearly all were green. Most of the leaves had burned and if still retained were nearly ready to drop from the plants in the 150-sulfate beds.

- Milo: there were outstanding differences at time of harvest in the amount of burning of the milo leaves. At this stage the oldest leaves of the control plants had already died and the margins of the leaves successively higher up the stalk showed drying to a decreasing degree. Less than 25 percent of the leaf tissue was dead in the 50-sulfate milo bed and about 50 percent in the 250-sulfate; the plants in the 150-sulfate bed were intermediate.

- Alfalfa: except for a reduction in plant size and a tendency toward slightly smaller leaves, the alfalfa in the high-sulfate beds lacked outward leaf symptoms indicative of salt injury. The margins of some leaves in the salt beds turned white in a narrow band, but this symptom cannot be regarded as specific, since it has been observed in fields and in other experiments where high salt conditions did not exist. The last two crops of alfalfa began to flower irregularly earlier in the sulfate-treated beds than in the control bed.

- Cotton: growing in the high-sulfate beds were reduced in size and the leaves were somewhat smaller than the controls, but otherwise all were normal in appearance. Symptoms of injury or other abnormalities were lacking.

- Tomatoes: aside from the prevalence of blossom-end rot on the tomatoes, sulfate salt did not produce symptoms of injury.

- Barley: the tips of older leaves of barley plants under sulfate treatments were burned considerably, and this burning was more pronounced with the higher concentrations.

- Sugar beets: the leaves in all beds were normal in appearance.

GROWTH-DEPRESSION GRAPHS

The growth-depression curves showed no evidence of an abrupt point at which toxicity effects became pronounced. It was indicated instead that above some minimum concentration each successive unit of salt, if considered by itself, tended to produce a lesser depression in growth than the preceding unit.

PLANT SAP EXAMINATION

ACCUMULATION

All crops accumulated relatively high concentrations of cations from the base nutrient solution, but the concentrations in milo, for example, were only approximately one-half as great, on all solutions as those in cotton. The concentration of total bases in the sap of milo and cotton in the control bed was, respectively, 18.2 and 34.8 times as great as in the nutrient solution.

Alfalfa, tomatoes and sugar beets occupied intermediate positions.

The total concentration and, in most instances, the concentration of individual ions in the sap were greater in plant’s grown in the salt beds than in the control bed, but it is to be noted that the accumulation ratios decreased with the addition of salt. The milo and cotton, with accumulation

ratios of 18.2 and 34.8, respectively, for total bases in the control bed, had ratios of 1.8 and 3.5, respectively, in the 250-sulfate bed.

Ratios unity show that the sap concentration of the salt plant was greater than that of the control plant, but that the increment was less than the quantity added to the base nutrient.

In contrast to the high accumulation ratios found in the control bed, sodium excepted, the increment ratios are usually low; the values are more often below unity than above.

Except for the sugar beets in all salt beds and alfalfa in the 50-sulfate bed, no plant increased the sodium concentration in its sap by as much as the solution was increased.

FREEZEN-POINT DEPRESSION

With each addition of sulfate salt to the base nutrient solution there was in general an increase in the osmotic pressure of the expressed sap. These increases in the freezing-point depression of the sap tended to parallel the corresponding increases in the freezing-point depression of the culture solutions. In some instances the sap increases exceeded the increases in the solutions and in other instances they fell below. If the six crops are viewed collectively, by means of averages the gains in differentials are balanced by losses, which would indicate little basis for a generalization that plants on saline soils are at a disadvantage in their water relations. The view has sometimes been expressed that plants are injured by salt because of the high osmotic pressure in soil solutions and the consequent limitation to water uptake.

WATER REQUIREMENT

Decreased water requirements were found for the 50-sulfate beds and water requirements higher than those of the controls were found for the 250-sulfate beds. Increased sap concentrations are conducive to reduced transpiration rates, but because of the reduction in growth caused by salt, exposure to light and wind was increased and this resulted in increased. The subject of blossom-end rot of tomatoes is somewhat irrelevant to the principal topic of this paper, but this disorder, absent from the control bed, became a factor of importance transpiration in plant growth in the sulfate beds, particularly in the latter. In the 250 -sulfate bed, 84 percent of the fruit was affected. Although the possibility that high chloride and high sulfate were independent causes cannot be entirely eliminated, the data suggest that calcium and magnesium accumulation singly or combined were important contributing factors.

There was little difference in the osmotic differentials between culture solutions and the leaves of tomatoes in any of the beds. Wilting of the tomatoes was not observed in any of the beds, but if incipient wilting did occur at any time as a result of insufficient moisture the chances for its occurrence would be greater in the control bed, from which there was greater water loss and in which there was no blossom-end rot.

For the leaves to withdraw water from the fruits it would be necessary to assume a water deficit in the leaves since, irrespective of osmotic differentials, a turgid cell is limited in its expansion and water uptake by the cell wall which bounds the protoplast. In other words, it would not be reasonable to assume that a significant amount of water could be withdrawn from fruits by turgid leaf cells.

PLANTS INJURY IN RELATION TO SALT ACCUMULATION

The addition of sulfate salt to the base nutrient resulted in a depression in the growth of nearly all plants and in the accumulation of sulfate in the sap in excess of the concentrations found in the control plants.

Applicant's summary and conclusion

Conclusions:

The growth-depression curves showed no evidence of an abrupt point at which toxicity effects became pronounced. It was indicated instead that above some minimum concentration each successive unit of salt, if considered by itself, tended to produce a lesser depression in growth than the preceding unit.

Executive summary:

A series of crop plants was grown to maturity in each of six large outdoor sand cultures supplied with a base nutrient and with sulfate salt (50 percent as sodium) added, in milliequivalents per liter, as follows: Control, 50-sulfate, 150- sulfate and 250-sulfate.

Results

Barley, milo and navy bean leaves were burned by sulfate salts and occasional lemon leaves were burned. Alfalfa, cotton, tomato, and beet plants showed no burning of the leaves nor were there symptoms of diagnostic significance other than a reduction of leaf size in cotton and severe blossom-end rot of tomatoes. The addition of sulfate salt to the base nutrient resulted in a depression in the growth of nearly all plants and in the accumulation of sulfate in the sap in excess of the concentrations found in the control plants.

The growth-depression curves showed no evidence of an abrupt point at which toxicity effects became pronounced. It was indicated instead that above some minimum concentration each successive unit of salt, if considered by itself, tended to produce a lesser depression in growth than the preceding unit.