Ethylene

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1968

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, non-guideline study, the methodology employed sound experimental principles and sufficient description of the procedure to assess the data as valid.

Qualifier:

no guideline followed

Principles of method if other than guideline:

21-hour old plants were contained at 25˚C in gas collection bottles with unsaturated gases added. Immediately after excision, and at 24 hours after venting and resealing, explants were surrounded by carbon dioxide, which was then removed from the gas collection bottles by KOH and filter paper wicks. At 48 hours, plants were analysed for abscission.
The interaction of carbon dioxide and ethylene was analysed by adding various concentrations of the two gases into the chambers. After the plants were excised, at 5 hours the chambers were vented to remove wound ethylene, at 21 hours the gas mixtures were added, and at 25 hours abscission was measured.
Warburg manometric techniques were used to analyse how oxygen uptake is affected by oxygen. Plants were stored for 19 hours in gas collection bottles covered with cheesecloth, before the bottles were sealed and flushed with nitrogen, then oxygen with 0.1 ppm ethylene and after 4 hours, abscission was measured. Explants were stored in petri dishes for 24 hours before being placed in bottom of the Warburg flasks. Commercial gases were used to prepare the oxygen-nitrogen mixtures and concentrations were determined by gas chromatography. Stationary manometers were used to measure respiration through oxygen consumption in the absence of carbon dioxide at 25°C.

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
Oxygen-nitrogen mixtures in the respiration control were prepared from commercial gases and stored under pressure in a steel container fitted with appropriate control valves. Gas chromatography was used to show that with less than 0.01 ppm ethylene in the carbon dioxide in the control experiment, the gases were below levels that would interfere with their use.

Analytical monitoring:

yes

Details on sampling:

Abscission was measured 4 hours after adding the respective gas mixtures in both the standard and respiration tests and at 48 hours in the control groups.

Vehicle:

yes

Details on preparation and application of test substrate:

No data reported

Species:

Phaseolus vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Bean (Phaseolus vulgaris L. cv. Red Kidney) plants aged 21 hours

Species:

other: Coleus explant (Coleus, Blumei Benth)

Plant group:

Dicotyledonae (dicots)

Species:

other: Cotton explants (Gossypium hirsutum L.cv. Acala 4-42)

Plant group:

Dicotyledonae (dicots)

Species:

other: Cassia explant (Cassia fistula L.)

Plant group:

Dicotyledonae (dicots)

Test type:

other: Abscission of young plants

Study type:

laboratory study

Substrate type:

not specified

Limit test:

no

Total exposure duration:

4 h

Post exposure observation period:

No data reported

Test temperature:

25°C

pH:

No data reported

Moisture:

No data reported

Details on test conditions:

Bean plants (Phaseolus vulgaris) were exposed to ethylene for 4 hours in gas collection bottles at 25 deg C. Immediately after excision, carbon dioxide was added to the gas phase surrounding the explants and then removed from the control atmospheres by KOH and a filter papaer wick.

Nominal and measured concentrations:

No data reported

Key result

Species:

Phaseolus vulgaris

Duration:

4 h

Dose descriptor:

EC50

Effect conc.:

0.1 other: ppm

Nominal / measured:

meas. (not specified)

Conc. based on:

other: Gas phase concentrations of ethylene in carbon dioxide

Basis for effect:

other: abscission

Details on results:

Half-maximum stimulation of abscission was found to be caused by approximately 0.1 ppm ethylene, with all other gases showing less activity. Carbon dioxide blocked abscission of the plants, though the effect could be reversed by simultaneous addition of ethylene, with higher concentrations required to overcome higher concentration of carbon dioxide.

Results with reference substance (positive control):

Respiration but not abscission increased when oxygen concentrations were increased above 21%. At low oxygen concentrations, the inhibition of abscission was the same or less than the inhibition of respiration. Tests showed that respiration was not significantly affected by up to 85ppm ethylene. Half-maximum amounts of ethylene (0.1ppm) showed that oxygen had no observable effect on ethylene production from the explants.

Reported statistics and error estimates:

Contamination of the test gases with ethylene was not reported, but may account for the greater activity of acetylene and 1-butene.

N/A

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study

Conclusions:

Half-maximum stimulation of abscission (natural separation of flowers, fruit or leaves) was caused by approximately 0.1 ppm ethylene, though other gases showed less activity. Abscission of the plants was blocked by carbon dioxide, though the effect could be reversed by simultaneous addition of ethylene. Half-maximum amounts of ethylene (0.1ppm) showed that oxygen had no observable effect on ethylene production from the explants.

Executive summary:

This is a non-GLP, non-guideline study that follows sound scientific principles. The study tested a variety of plants under strict conditions, with analytical monitoring and control groups. The report is considered reliable and suitable for use for this endpoint.

Reference 2

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1973

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-GLP, non-guideline, the methodology employed sound experimental principles and sufficient description of the procedure to assess the data as valid

Qualifier:

no guideline followed

Principles of method if other than guideline:

Three tests were carried out. Reversibility measured the percentage of leaf abscission by applying a gentle force to the surface of the petiole of cotton or by gently shaking the plant in the case of bean and measuring auxin transport capacity using the donor-receiver agar cylinder technique. Temperature sensitivity measured abscission and auxin transport in plants which had been exposed to ethylene for 24 hours in the dark at temperatures ranging from 8 to 31.5°C. Auxin pretreatment measured auxin transport capacity in sections cut from the basal end of the petiole of plants treated with naphthalene acetic acid after they had been exposed to ethylene for 24 hours.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
No data reported

Analytical monitoring:

yes

Details on sampling:

Reversibility experiments monitored auxin transport capacity before, during, and after ethylene treatment. Auxin pretreatment experiments measured auxin transport after exposure to ethylene for 24 hours.

Vehicle:

no

Details on preparation and application of test substrate:

No data reported

Species:

other: Cotton seedlings plants (Gossypium hirsutum L. cv. Stoneville 213)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Cotton plants were grown in plastic pots up to an age of 20, 23, or 25 days old in a controlled environment (temperature 27±1°C (day) and 21± 1°C (night); relative humidity 56% night and 50% day; 14-hr photoperiod; watered daily).

Species:

Phaseolus vulgaris

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Bean plants (Phaseolus vulgaris L. cv. Resistant Black Valentine)
Information regarding the culturing of bean plant was not included. Plants: 9 or 10 day old.

Test type:

other: Reversibility and temperature sensitivity of ethylene and auxin in abscission

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

72 h

Remarks:

Reversibility experiment: 48hr; Temperature sensitivity experiment: 24 hr

Post exposure observation period:

Auxin transport capacity and abscission were measured at periodic intervals throughout the experiment.

Test temperature:

Reversibility experiment: 28.5 ± 1°C day and 21± 1°C night
Temperature sensitivity experiment: range from 8 to 35°C

pH:

No data reported

Moisture:

75% day and 55% night

Details on test conditions:

In the reversibility experiments, plants were placed in an acrylic chamber with a photoperiod of 14 hours and a constant flow rate of ethylene for 24 or 48 hours before being transferred into a second chamber with only air. CO2 levels were controlled by KOW and filter paper wicks.

Nominal and measured concentrations:

One chamber had a flow rate of 8.5L/min with 14µl ethylene/ L air as determined by gas chomatography, while a second chamber had only air with < 5 nl/l ethylene.

Key result

Species:

Phaseolus vulgaris

Duration:

72 h

Dose descriptor:

other: Not Specified

Effect conc.:

ca. 14 other: µL ethylene/ L air with a flow rate of 8.5 L/min

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: leaf abscission

Remarks on result:

not measured/tested

Remarks:

Transport inhibition was significantly greater in the stems than in the petioles after 24 hours, when measured in the same plants simultaneously. However, the percentage of abscission was not always reproducible under the same conditions.

Key result

Species:

other: Cotton seedlings plants (Gossypium hirsutum L. cv. Stoneville 213)

Duration:

72 h

Dose descriptor:

other: Not specified

Effect conc.:

ca. 14 other: µL ethylene/ L air with a flow rate of 8.5 L/min

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: leaf abscission

Remarks on result:

not measured/tested

Remarks:

Transport inhibition was significantly greater in the stems than in the petioles after 24 hours, when measured in the same plants simultaneously. However, the percentage of abscission was not always reproducible under the same conditions.

Details on results:

Reversibility: Transport inhibition was significantly greater in the stems than in the petioles after 24 hours, when measured in the same plants simultaneously. However, the percentage of abscission was not always reproducible under the same conditions. Significant but never full recovery of both cotton and bean plants occurred when transferred to air after 24 hour exposure to ethylene. The extent of recovery was dependent on the length of ethylene treatment.

Results with reference substance (positive control):

Temperature sensitivity: Two separate experiments of this type were conducted. A 24 -hour exposure of intact plants to temperatures ranging from 8 to 31.5°C had no significant effect on the subsequent transport of auxin. Increasing the temperature above 8 deg C resulted in a progressively greater reduction in auxin transport capacity. However, the data show that the total amount of auxin transport cannot solely govern the magnitude of ethylene inhibition. Therefore, measuring transport capacity at a constant temperature rather than at the temperature of ethylene treatment avoided the complicating effect of temperature on auxin transport.
Auxin Pre-treatment: Naphthalene acetic acid (NAA) pretreatment severely reduces the effect of ethylene on auxin transport compared to the control plants.

Reported statistics and error estimates:

No data reported

Results indicate that inhibition of auxin transport was much more significant in the stems than petioles, though analysis indicated that this was not caused by auxin destruction during transport, differences in auxin uptake or inherent differences in auxin capacity. Abscission in cotton and bean plants exposed to ethylene has been found to be a reversible process. In cotton plants complete recovery occurred within 5 days for stems and 3 days for petioles after an ethylene exposure of 24 hours. Increases in the duration of ethylene exposure lead to increases in abscission, up to 100% after 4 days. However, in bean plants, the process is not completely reversible and the length of ethylene exposure determined the extent of the recovery. There was also no significant difference between the stems and petioles in the rate of initial recovery. The effect of ethylene exposure on beans was significantly less than cotton plants, with no abscission and less than 50% auxin transport inhibition after 24 hours exposure, though complete abscission occurred in only 3 days.

Abscission in plants exposed to ethylene increased from none at 21.5˚C to over 70% at 31.5˚C. The effect of exposure on auxin transport increased with increasing temperature, from no effect at 8˚C. Results show that transport inhibition is not only governed by the transport capacity as the greatest changes in these two responses occur at different temperature ranges.

Results indicate that auxin pre-treatment the effect of ethylene on auxin transport is reduced for both intact plants and excised sections. In contrast, auxin transport of plants in air was not significantly affected by auxin pre-treatment.

Validity criteria fulfilled:

not applicable

Conclusions:

Cotton and bean plants placed in 14 ul/L of ethylene for 24 or 48 hours showed an increase in leaf abscission and reduced capacity to transport auxin, effects which increased with increased temperature. Auxin pretreatment reduced ethylene-induced abscission and auxin transport inhibition. The auxin transport system of cotton plants exposed to ethylene for 24-hours then transferred to air showed recovery. Beans also showed significant recovery in the 24 hours after exposure, however full recovery did not occur. The extent of recovery was dependent on the length of ethylene treatment.

Executive summary:

This is a non-GLP, non-guideline published study. The experiment follows sound scientific principles, testing the reaction of auxin transport systems to plant exposure to ethylene, inlcuding the use of control groups. The study is considered reliable and suitable for use for this endpoint.

Reference 3

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1973

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-GLP, non-Guideline, the methodology sound experimental principles and sufficient description of the procesure to assess the data as valid.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Plants exposed to reagent grade ethylene at set concentrations were grown in Plexiglass chambers. Abscission of plant leaves, to which 5g weights were applied, was measured at 12 or 24 hours after exposure. 24 hours prior to exposure, a proportion of plants were treated with auxin inhibitor.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
Auxin transport inhibitors DPX-1840 (3,3a-dihrdro-2-(p-methoxyphenyl-8H pyrazzolo-(5,1-a) isoindol-8-one), triiodobenozoic acid, soldium N-1-naphthylphthalamate and morphactins all produced similar results when applied to plants as an aqueous spray 24 hours prior to exposure.

Analytical monitoring:

yes

Details on sampling:

Each treatment was applied to 2 to 4 pots containing 3 or 4 plants.

Details on preparation and application of test substrate:

No data available

Species:

other: Vegetative cotton (Gossypium hirsutum L.)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Seedlings were grown for 26 days in a greenhouse until 2 to 4 open true leaves developed.

Test type:

other: leaf abscission in plants

Study type:

laboratory study

Substrate type:

not specified

Limit test:

no

Total exposure duration:

4 d

Post exposure observation period:

Not reported

Test temperature:

27°C day and 25°C night

pH:

not reported

Moisture:

Plants were watered daily in a non-humidity controlled environment.

Details on test conditions:

Chambers were maintained at 30±1°C over the 15 ‘daylight’ hours. CO2 build-up was prevented by including KOH with paper towel wick in the chambers.

Nominal and measured concentrations:

0.1 to 51.2µl ethylene / l air

Reference substance (positive control):

not specified

Key result

Species:

other: Vegetative cotton (Gossypium hirsutum L.)

Duration:

96 h

Dose descriptor:

other: sensitivity to ethylene

Effect conc.:

ca. 0.1 - ca. 51.2 other: µL ethylene / L air

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Leaf abscission

Remarks:

N/A

Remarks on result:

not measured/tested

Remarks:

For each plant age, there was a region of maximum sensitivity to ethylene, generally the first partially expanded leaf and those above it, then a second region at the base of the plant that moved upward with time. The effect was most pronounced in the oldest plants and higher ethylene levels.

Details on results:

Ethylene was exposed for 96 hours to 11, 19, 26, and 33 day old plants. In older plants, extensive abscission occurred earlier for both 1.96 and 10.25 µl /l air concentrations tested. However, in the two oldest groups, age induced differenced decreased. In all groups, the youngest opened leaves abscised first, followed by those above it. However, in the oldest plants, partially expanded apical leaves, cotyledons and oldest true leaves were abscised first and, at the highest levels of ethylene, to a greater extent.

Results with reference substance (positive control):

With the auxin transport inhibitor DPX-1840 applied, the oldest true leaf was abscised only a little or not at all, with cotylendonary leaves and leaves 2 and 3 abscission promoted instead.

Reported statistics and error estimates:

N/A

The maximum sensitivity to ethylene occurred from top down to the first partially expanded leaf, with a second sensitivity region moving upwards from the plant’s base. The sensitivity of basal leaves increased with older plants and higher concentrations of ethylene.

Validity criteria fulfilled:

not applicable

Conclusions:

The abscission of younger leaves of cotton plants increases with age and the concentration of ethylene, and is promoted by anuxin transport inhibitors. Abscission changes to oldest leaves after the initial loss of unexpanded leaves. The results of the study indicate that apical leaves have an increased sensitivity to ethylene, which may be caused by a difference in hormone complements or a difference between expanded and unexpanded leaves on the abscission process.

Executive summary:

This is a non-GLP, non-guideline published study, which follows sound scientific principles. Leaves from plants between 2 and 5 weeks old were exposed to set concentrations of ethylene, with some experiments also exposed to auxin inhibitor. Weights were placed on the leaves and presence and variation of abscission was analysed. The study is considered reliable and suitable for use for this endpoint.

Reference 4

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2002

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, non-guideline, the methodology employed sound experimental principles and sufficient description of the procedure to assess the data as valid

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study site, located within an industrial zone close to 5 ethylene-emitting chemical plants, was divided into grids with biomonitoring stations at the intersections. The number of flowers and vegetative growth was visually estimated according to 4 growth indices: 0 (unaffected), 1 (slightly reduced growth, no adverse effects on flower formation), 2 (growth reduced and adverse effects on flower formation), 3 (dwarfed growth and flowers desiccated or completely absent). Data were averaged over a 10-week growth period when there was maximal flowering for each species.

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
There were 2 control sites situated in a rural area unlikely to have been influenced by the chemical plant emissions or other potential sources. Mean hourly ethylene concentrations at the control sites prior to the study period generally ranged below 10 ug/m3. Control plants were assumed to grow well (growth index =0).

Analytical monitoring:

yes

Details on sampling:

Monitoring was conducted over several years from 1977 to 1983, during which the number and location of the biomonitoring stations changed, but at study termination there were 49 stations, which had moved to a final location that was further from the chemical plants than when the study began.
Measurements were recorded weekly between early June and late September.

Vehicle:

no

Details on preparation and application of test substrate:

The study site was 1800 m long, in the direction of the prevailing wind, and 800 m wide. The site was divided into grids of 200x200 m squares and the biomonitoring stations located at points where the grids intersected. Three containers of plants were placed in one larger container (one container per site per year of observation), that was placed at the soil surface and served as a water reserve.

Species:

other: Petunia nuctaginiflora Juss. cv. White Joy (petunia)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Petunia nuctaginiflora Juss. cv. White Joy (petunia) were purchased from a plant nursery each year of the study and transplanted into standard potting soil in plastic containers with ceramic filter watering devices to automatically maintain soil moisture. Plants were allowed to grow at the study and control sites during the growing season. At each site, two plants of petunia were grown in one container.

Species:

other: Tagetes erecta L. cv. Sovereign (marigold)

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

Tagetes erecta L. cv. Sovereign (marigold) were purchased from a plant nursery each year of the study and transplanted into standard potting soil in plastic containers with ceramic filter watering devices to automatically maintain soil moisture. Plants were allowed to grow at the study and control sites during the growing season. At each site, three plants of marigold were grown in each of two containers.

Test type:

other: Flowers and vegetative growth comparisons

Study type:

semi-field study

Substrate type:

natural soil

Limit test:

no

Total exposure duration:

4 mo

Remarks:

Growing seasons of 1977 to 1983

Post exposure observation period:

No data reported

Test temperature:

No data reported

pH:

No data reported

Moisture:

Ceramic filter watering devices were used to automatically maintain soil moisture.

Details on test conditions:

No data reported

Nominal and measured concentrations:

At a monitoring station 1000 m downwind of the emission sources, hourly values of ethylene ranged from a high of 7276 ug/m3 in 1982 to 307 ug/m3 in 1983. This was equivalent to a growing season mean of 61.5 ug/m3 in 1982 and 15.6 ug/m3 in 1983.

Key result

Species:

other: Petunia nuctaginiflora Juss. cv. White Joy (petunia)

Duration:

4 d

Dose descriptor:

other: Reduction in flower formation, plant growth and plant performance.

Effect conc.:

ca. 15.6 - ca. 61.5 other: µg/m3 growing season means for 1982 and 1983

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

other: Reduction in flower formation, plant growth and plant performance.

Remarks on result:

not measured/tested

Remarks:

Flower formation and plant growth were severely reduced close to the emission sources and plant performance improved with increased distance from the source. Plants were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering. Petunia was more sensitive than marigold in terms of number of flowers.

Key result

Species:

other: Tagetes erecta L. cv. Sovereign (marigold)

Duration:

4 d

Dose descriptor:

other: Reduction in flower formation, plant growth and plant performance.

Effect conc.:

ca. 15.6 - ca. 61.5 other: µg/m3 growing season means for 1982 and 1983

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

other: Flower formation, plant growth and plant performance

Remarks on result:

not measured/tested

Remarks:

Flower formation and plant growth were severely reduced close to the emission sources and plant performance improved with increased distance from the source. Plants were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering.

Details on results:

Flower formation and plant growth were severely reduced close to the emission sources and plant performance improved with increased distance from the source. Plants were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering. Petunia was more sensitive than marigold in terms of number of flowers.

Results with reference substance (positive control):

More flowers were observed at the border of the research area than in the control site, with an increase of up to 71 and 58% for marigold and petunia sites respectively.

Reported statistics and error estimates:

The number of flowers per species relative to the control was calculated for each station and year. The real distance to the source was calculated for each biomonitoring station in all directions. To test for significant effects due to distance, plant species and their interaction, data on flowering were subjected to linear regression analyses with distance as the variate and plant species as a classifying factor. Data on growth were subjected to linear regression analyses with distance as variate only. Prior to these analyses, data were adjusted for the overall effect of year.

For both plant species, flower formation and growth were severely reduced and plants showed dwarfed growth, desiccation of flower buds and absence of flowers at sampling stations closest to the emission sources. Plant performance improved with increasing distance from the emission sources to show no adverse anomalies furthest from the emission sources. The furthest plants had normal growth and more flowers than the unexposed controls. Statistical analyses showed that the number of flowers at each site depended significantly on distance from the sources and differed between plant species.
At a monitoring station 1000 m downwind of the emission sources, hourly values of ethylene ranged from 7276 ug m^-3to 307 ug m^-3, equivalent to a growing season mean of 61.5 ug/m3 in 1982 and 15.6 ug/m3 in 1983, while the growth indices were 0.14 and 0.08, respectively. Petunia was more sensitive than marigold and adverse effects were observed within approximately 400 m and 460m distance from the emission sources respectively. The area at risk (up to approximately 870 m from the emission sources) for ethylene-induced growth reduction was also limited to within the industrial zone. Plants were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering.

Validity criteria fulfilled:

not applicable

Remarks:

non-guideline study

Conclusions:

The study showed that flowering was stimulated and growth was not affected in petunia and marigold plants exposed to a growing season mean of 62 ug/m3. Adverse effects were observed within approximately 400 m distance from the emission sources for marigold and within approximately 460 m for petunia, with the area at risk being up to approximately 870 m from the emission sources. The plants tested were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering.

Executive summary:

This is a non-GLP, non-guideline study. The methodology employed sound experimental principles and sufficient description of the procedure to assess the data as valid. The study is considered reliable and suitable for use for this endpoint.

Reference 5

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

May to September 2001

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-GLP, non standard methodology, sound experimental principles, acceptable with restrictions

Principles of method if other than guideline:

Open top chambers were used to carry out field experiments. In one series of tests atmospheric ethylene was exposed to the plants at set concentrations either twice or four times a week for three hours. In another series of tests, realistic concentrations of ethylene were exposed to potato plants for an entire growing season. The estimated effect threshold and the predicted worst case scenario were estimated using models simulating crop growth.

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
LINTUL is a model simulating crop growth, with parameters developed from experimental data. The model was used to predict the extent to which ethylene would affect growth of crops and tuber production.

Details on sampling:

The effects of ethylene were measured through variation mainly in epinasty and the number of flower clusters. The canopy ground cover, crop height and height of senescent leaves have also been measured, along with the proportion of plants that do not survive. The growth of tubers and the dry weights of the leaves and stems were also measured during the crop harvest.

Details on preparation and application of test substrate:

The field experiments were carried out in open top chambers, each of which had a volume of 3.7 m3 and a soil area of 1.95 m2. The soil areas were prepared using common farming practices of mixing clay soil and fertiliser and spreading over the surface to a depth of 40 cm.

Species:

other: Solanum tuberosum L.

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

The potato plant was chosen for this experiment as large amounts of data are available concerning its physiology and production and it has been shown by Taylor et al (1987) to be sensitive to atmospheric ethylene. A model already exists for the response of potato plants to atmospheric ethylene from emission sources.

Test type:

other: field experiment over entire growing season

Study type:

other: model and field study

Substrate type:

natural soil

Limit test:

no

Total exposure duration:

4 mo

Remarks:

Exposure period: growing season

Post exposure observation period:

Within the timeframe of the experiment, post-exposure observation was possible due to the discontinuous application of ethylene.

Test temperature:

Day/night temperature of 15/10 deg C

pH:

No data available

Moisture:

Plants were watered with tap water as required. Optimal growing conditions were provided through application of disease control.

Details on test conditions:

Ethylene treatments were applied from 6 days after planting. The open top chambers allowed a wind speed of 1-1.5 ms-1 at plant level and formed of UV-B absorbent plastic though shade nets were also applied.

Nominal and measured concentrations:

The air in the chambers was replaced approximately 3.6 times very minute. Plants were treated with 6 discontinuous treatments over 3 hours of different concentrations and/or frequency, each repeated three times. The treatments were applied either 2 or 4 times a week at concentrations of ambient air (control), 200, 400, and 800 ppb.

Reference substance (positive control):

no

Key result

Species:

other:

Duration:

4 mo

Dose descriptor:

NOEC

Effect conc.:

< 10 other: ppm

Nominal / measured:

nominal

Conc. based on:

other: ambient ethylene concentrations at the field site

Basis for effect:

other: Potato yield and other harvest parameters (e.g. potato size class or misformed potatoes).

Remarks on result:

other: Duration: growing season

Details on results:

24 hours after exposure to ethylene in the dark, potato plants exhibited a 14% decrease in photosynthesis, though within 3 days, photosynthesis rates had completely recovered. Plant respiration rates in the dark increased following exposure, but this was reversed within approximately 24 hours.

Results with reference substance (positive control):

After exposure to ethylene in the light, photosynthesis initially increased, then decreased over time. When then placed in the dark, photosynthesis rates were maintained at a higher level than prior to experiment initiation. Results indicate that plants have a steeper decline in stomatal conductance and slower recovery when exposed to ethylene in the light.

Reported statistics and error estimates:

Results were analysed for the effects of ethylene concentration and exposure frequency, with raw data square root transformed in order to stabilise variance. Students’ t-tests with statistical significance of P<0.05 were conducted for variations in exposure.

In contrast to ambient concentrations of 10 ppb ethylene, exposure concentrations were 216.8, 405.3 and 792.9 ppb for 2 weeks or 217.7 and 402.0 ppb for 4 weeks. Half of the exposures were conducted between midnight and 3am and half between 11am and 2pm. Results of exposure included a decrease in flowers, from 100 to 15 with an increase in ethylene exposure from 200 to 800 ppm, as well as epinasty, though variations in severity were irrespective of exposure concentrations. The harvest yield, potato size or proportion of malformed potatoes was not affected by ethylene concentration or frequency of exposure.

Validity criteria fulfilled:

not applicable

Conclusions:

The experiment results indicate that potato plants and harvest yield were unaffected when exposed for 3 hours 4 times a week to ethylene concentrations up to 800 ppb. This discontinuous exposure produced a much higher threshold than the 10 ppb continuous exposure shown by Abeles and Heggestad (1973). These results imply that discontinuous exposure allows plants to recover between exposure periods and thus plants exposure outdoors are often less sensitive than indoor grown plants.

Executive summary:

This is a non-GLP compliant, non-guideline study, which follows sound scientific principles. The experiment covers the entire growing season of the test plant with realistic discontinuous exposure to ethylene in open top chambers and analyses both growth and harvest parameters. The study is considered reliable and suitable for use for this endpoint.

Reference 6

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

See attached justification

Qualifier:

no guideline required

Principles of method if other than guideline:

The endpoints calculated are the LL50, EL50, and NOELR -
The narcosis target lipid model was developed to predict the toxicity of chemicals to aquatic organisms that act via narcosis. It is based on the hypothesis that target lipid is the site of toxic action within the organism, that octanol is the appropriate surrogate, and that target lipid has the same physical–chemical properties in all organisms.
The approach describes:
• The theory and how to predict the acute toxicity to these organisms;
• Development of an Acute to Chronic ratio [ACR] for only hydrocarbons and for 29 data points.

GLP compliance:

no

Specific details on test material used for the study:

NA

Analytical monitoring:

not required

Details on sampling:

N/A

Details on preparation and application of test substrate:

N/A

Species:

Brassica rapa

Plant group:

Dicotyledonae (dicots)

Species:

Avena sativa

Plant group:

Monocotyledonae (monocots)

Post exposure observation period:

N/A

Test temperature:

N/A

pH:

N/A

Moisture:

N/A

Details on test conditions:

N/A

Nominal and measured concentrations:

N/A

Key result

Species:

Avena sativa

Duration:

14 d

Dose descriptor:

other: LL50

Effect conc.:

75.35 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

seedling emergence

Key result

Species:

Avena sativa

Duration:

21 d

Dose descriptor:

other: NOELR

Effect conc.:

14.43 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Key result

Species:

Brassica rapa

Duration:

14 d

Dose descriptor:

other: LL50

Effect conc.:

48.65 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

seedling emergence

Key result

Species:

Brassica rapa

Duration:

21 d

Dose descriptor:

other: NOELR

Effect conc.:

9.32 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Details on results:

N/A

Results with reference substance (positive control):

N/A

N/A

Validity criteria fulfilled:

yes

Conclusions:

The estimated LL50 values for this substance were 75.35 and 48.75 mg/kg soil dw and estimated NOELR values were 14.434 and 9.32 mg/kg soil dw to Avena sativa and Brassica rapa, respectively.

Executive summary:

The registered substance is highly volatile which complicates environmental testing. Therefore, a modeling framework is needed to account for the bioavailability of the substance to perform read-across and data gap filling. The TLM-EqP modeling has been validated as a suitable method for predicting effect values in terrestrial plants. The TLM-EqP predicted effect values for ethylene were 75.35 and 14.43 mg/kg soil dw for short-term (14-day LL50) and long-term effects (21-day NOELR) to Avena sativa, respectively. The TLM-EqP predicted effect values for ethylene were 48.65 and 9.32 mg/kg soil dw for short-term (14-day LL50) and long-term effects (21-day NOELR) to Brassica rapa, respectively.

Description of key information

The 4 month (growing season) NOEC for exposure of potato plants to ambient ethylene concentrations was <10 ppm (nominal) based on yield and harvest parameters.

The estimated LL50 values from TLM QSAR modelling for this substance were 75.35 and 48.65 mg/kg soil dw and estimated NOELR values were 14.43 and 9.32 mg/kg soil dw to Avena sativa and Brassica rapa, respectively.

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:

48.65 mg/kg soil dw

Long-term EC10, LC10 or NOEC for terrestrial plants:

9.32 ng/kg soil dw

Additional information

Exposure to above soil plant parts is more relevant than exposure to soil and the effects of ethylene on plants are well understood.

The available data have been taken from published, non-GLP, non-guideline papers, which all follow sound scientific principles and include sufficient description of the procedure to assess the data as valid. The studies tested a variety of plants over a range of time periods, under strict conditions with analytical monitoring and control groups. The studies are considered reliable and suitable for use for this endpoint.

Dueck (2003) showed ethylene concentrations of up to 800 ppb, administered 4 times per week for 3 hours during the growing season, did not affect vegetative growth and yield in the exposed potato plants. Plants exposed to discontinuous exposures of ethylene outdoors are given ample time for recovery and possible compensation.

Morgan (1973) showed that for each plant age there was a region of maximum sensitivity to ethylene, generally the first partially expanded leaf and those above it, then a second region at the base of the plant that moved upward with time. The effect was most pronounced in the oldest plants and higher ethylene level.

Elmo and Beyer (1973) showed an increase in leaf abscission and reduced capacity to transport auxin in plants exposed to 14 uL/L of ethylene for 24 or 48 hours. Effects increased with increased temperature and were reduced with auxin pre-treatment. The auxin transport system showed full recovery in cotton plants, but only significant recovery in beans, with recovery level dependent on ethylene concentration.

Abeles (1968) showed half-maximum stimulation of abscission at approximately 0.1 ppm ethylene. Abscission of the plants was blocked by carbon dioxide, though the effect could be reversed by simultaneous addition of ethylene; oxygen had no observable effect on ethylene production.

Tonneijck (2003) showed in plants exposed to a growing season mean of 62 µg ethylene/m³ that flowering was stimulated and growth was not affected. Adverse effects were observed to diminish with distance to 870 m from the emission sources, though growth reduction was more sensitive than flowering inhibition.