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Toxicity to terrestrial plants

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Description of key information

Two keys studies were performed according to OECD 208 guideline on three different species. The lowest EC50 was measured for shoot growth of mung bean at 4.7 mg/kg DW and the NOEC was determined at 0.83 mg/kg DW for the three species. Nine other studies on hydroponic and atmosferic exposures of several plants species and on bioaccumulation of TFA supported these results. According to column 2 of REACH Annex X, long term toxicity study on plants does not need to be conducted for trifluoroacetic acid because direct and indirect exposure of soil is unlikely based on its low potential for adsorption to soil (log Kow = 0.79 and Kd= 0.94 L/kg at 25°C) and no risk was characterised for the soil compartement in the Chemical Safety Assessment according to Annex I.

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:
4.7 mg/kg soil dw
Long-term EC10, LC10 or NOEC for terrestrial plants:
0.83 mg/kg soil dw

Additional information

Two key studies were performed according to the testing OECD 208 guideline to measure the effect of sodium trifluoroacetate (NaTFA) in soil on seed germination and early plant growth of Sunflower (Helianthus annuus), Mung Bean (Phaseolus aureus) and Wheat (Triticum aestivum). Nine seeds per pot, in four replicates were sown in soil containing nominal concentrations of 1, 10, 100 and 1000 mg sodium trifluoroacetate / kg (dry soil) plus control.

There were statistically significant decreases in the proportion of seeds which had germinated and emerged after 14 days and the EC50s for germination were as follows:

Sunflower : EC50 germination = 250 mg NaTFA/kg (208 mg TFA/kg)

Mung Bean : EC50 germination = 770 mg NaTFA/kg (640.8 mg TFA/kg).

Wheat: EC50 germination= 1000 mg/kg NaTFA/kg

At the end of the test, 28 days after the seeds were sown, the mean fresh weight of the seedling shoots (cropped at soil level) were significantly reduced and the calculated EC50 for growth, based on nominal concentrations were as follows:

Sunflower : EC50, Shoot growth (28d) = 12 mg NaTFA/kg (10 mg TFA/kg).

Mung Bean : EC50, Shoot growth (28d) = 5.7 mg NaTFA/kg dry soil (4.7 mg TFA/kg).

Wheat: EC50 Shoot growth (28d) = 12 mg NaTFA/kg dry soil (10 mg TFA/kg dry soil).

There was no significant effect on shoot weight at 1 mg sodium trifluoroacetate / kg and therefore :

Sunflower : NOEC shoot weight (28d) < 1 mg NaTFA/kg (< 0.83 mg TFA/kg).

Mung Bean : NOEC shoot weight (28d) = 1 mg NaTFA/kg dry soil (0.83 mg TFA/kg).

Wheat: NOEC shoot weight (28d) = 1 mg NaTFA/kg dry soil (= 0.83 mg TFA/kg dry soil).

 

The toxicity of TFA is mainly observed when the seeds are sown and resulted in a reduced shoot growth. The germination is also impacted but at a lowest level. A NOEC of 1 mg/ kg dry soil NaTFA corresponding to 0.83 mg/kg dry soil TFA is safe for both stage.

 

The other studies reported were not been performed according to standard guidelines but they support the key studies results.

Four studies were performed under hydroponic conditions on different plant species. One study investigated the Soybean and show that the plants were developmentally stunted and had shoot weights that were significantly reduced above the NOEC shoot fresh weight (36d) = 0.674 µL TFA/kg soil ww (corresponding to 1mg TFA/kg soil ww). Further, the effect of seven halogenated aliphatic acids including TFA on the initial growth of wheat and tomato roots and shoots was studied.The results showed different sensitivity between the Monocotyledonae and the Dicotyledonae species. Wheat shoot was more inhibited than tomato shoot. Wheat root was not inhibited and Tomato root was more inhibited than tomato shoot. Also, the effect of TFA on seed germination of ten species by aqueous exposure were investigated. No effect on germination was found up to 832 mg TFA/L for all species. Finally, the toxicity to plantago major by aqueous exposure and a NOEC (14d), based on leaf or root weight, of 26.6 mg TFA/L was reported.

Three studies assessed as not assignable based on insufficiently documented reports investigated the TFA effects by atmospheric pathways. One study on several plants testing mist and rain deposition of TFA demonstrated a NOEC (25d) > 83,2 mg TFA/L for height and fresh weight on sunflower, soya, wheat, maize, oilseed rape, rice and plantain and LOEC (44d) = 83,2 mg TFA/L for visible injury on soya. Another study on the effect of TFA on wheat after pulverization shows 45% destruction on pre-emerging phase with 1.8 mg TFA/kg and 50% destruction on post-emerging phase with 7.4 mg TFA/kg. Finally one study performed onPinus ponderosaexposed to TFA applied as mist to foliar surfaces demonstrated an accumulation in needles as a function of concentration applied and no visual morphological or photosynthetic effects at 0,01 µg TFA/l. Further the results indicate that atmospheric uptake may not be the dominant pathway of uptake in environmental conditions but rather root uptake.

Finally, four other studies investigated the mode of action of TFA to plants. One study described the uptake of Trifluoroacetic acid in Lycopersicon esculentum using 19F and 1H nuclear magnetic resonance imaging and spectroscopy. The spectroscopy results show that the TFA is transported through the stem and accumulates in the leaves. Another study investigated the toxicity to wheat in relation to bioaccumulation by aqueous exposure of the roots to 14C-radiolabelled sodium trifluoroacetate for 35 days. The inhibition of the growth of plants including tissue chlorosis and necrosis was associated with an increasing 14C-residues levels in the leaf tissues over the period of exposure and a bioconcentration factor (BCF) of 43 after 35 days. In an other report, Sunflower seedlings were exposed to a single concentration of 14C-radiolabelled trifluoroacetic acid in the aqueous (hydroponic) medium. 14C-residues in the leaf tissues increased continuously over the period of exposure, with a bioconcentration factor (BCF) of approximately 22 after 12 days. The stem tissue behaved similarly but with a lower rate of accumulation (12 -day BCF approximately 5). Root tissue reached apparent equilibrium after 5 days exposure with a BCF of approximately 3. All tissues showed a decline in 14C-residue concentrations on transfer to clean medium with some evidence of depuration. In another study, growth and development of nitrogen-fixing soybean seedlings was assessed in the presence of trifluoroacetic acid in soil cultures. Overall the results show that TFA, at 1 mg/kg does not interfere with the ability of nitrogen-fixing bacteria to infect and colonize the plant, nor does it interfere with the normal development and nitrogen-fixation by the growing plant.

According to column 2 of REACH Annex X, long term toxicity study on plants does not need to be conducted for trifluoroacetic acid because direct and indirect exposure of soil is unlikely based on its low potential for adsorption to soil (log Kow = 0.79 and Kd= 0.94 L/kg at 25°C) and no risk have been characterised by the Chemical Safety Assessment according to Annex I. Moreover, the two terrestrial plant tests performed according to OECD 208 are assumed to cover a sensitive stage in the life-cycle of a plant and therefore data obtained from these studies have been used as estimates of chronic toxicty as mentionned in the Chapter R.7C of the Guidance on Information requirements and CSA of ECHA.