Iron sulphate

Toxicity to terrestrial plants

Description of key information

No relevant effects

Additional information

This endpoint is covered by the category approach for soluble iron salts (please see the section for physical and chemical properties for the category justification/report format). Testing for this endpoint has been waived in accordance with column 2 and Annex XI, part 3, restrictions.

There are no standard terrestrial toxicity tests reported in the literature, but results from several studies investigating effects of soluble iron salts applied directly to the soils are known from the literature. Such direct exposure of terrestrial plants to iron salts can be excluded in the supported uses and is therefore not in contradiction to the assessed absence of environmental toxicity of the submission item. Thus these experiments are not relevant as this exposure path is irrelevant for effects of the submission item to the environmental life. Uses of iron (II) sulphate (FeSO4) as an herbicide on amenity and sports turf for the control of moss (U.S. EPA 1993) are known, but require direct application of the salt, which circumvents the speciation processes in watery solution.

The following section is taken from the SIAR for iron salts (OECD 2007), Section 4.2: “Iron is an essential trace element for plant development being involved in chlorophyll formation (Remark: No reference given, but in line with U.S. EPA 2003), cell division and growth and as an oxygen carrier. Results reported by Singh & Prakash (1990), for a study assigned reliability 2, show increased iron uptake and biomass production in wheat (Triticum sp.) at direct application rates of up to 10 ppm Fe (i.e. [mg Fe/kg soil]) added as ferrous sulphate (FeSO4.7H2O). At 20 ppm measured iron uptake and biomass were reduced, as were phosphorous levels. This is consistent with iron reducing the availability of phosphorous. Mizuno et al (1993) reported a 10 % decrease in total biomass for a potato (Solanum tuberosum) crop at the very high ferrous sulphate (FeSO4) addition level of 800 kg/ha (290 kg Fe/ha). This test was carried out in an acidic soil, pH 4.6 - 5.0 which would significantly increase iron availability. It should also be noted that at this low pH toxic effects due to high aluminium levels are possible. The study has been assigned reliability 4. Yield of rice (Oryza sativa) was increased, in a reliability 2 study reported by Prasad & Singh (1988), by addition of Fe (as FeSO4.7H2O) at concentrations up to 12.5 ppm Fe. Yield was depressed at a concentration of 25 ppm (i.e. mg/kg) Fe. In a reliability 2 study reported by Subrahmanyam et al (1991), the addition of Fe (as Fe2(SO4)3) to soil at 5 and 10 ppm increased plant height and biomass in Corn mint (Menthe arvensis) relative to those at a concentration of 2.8 ppm.”

U.S. EPA (2003) considers the following literature data: “Efroymson et al (1997a) reviewed several studies which examined plant sensitivity to iron from soil solutions. Wallihan (1966) reported unspecified reductions in plant growth in a solution culture with the addition of 10 mg/L of iron. Wallace et al. (1977) evaluated the effects of iron (as FeSO4) on leaf, stem, and root weights of bush bean seedlings grown for 15 days in nutrient solution. Iron at 28 mg/L reduced all three measures 67, 52, and 67 %, respectively, while 11.2 mg/L had no effect. After 55 days, cabbage seedling plant weight was reduced 45 % by 50 mg/L Fe added as FeSO4 nutrient solution (pH 5), while 10 mg/L had no effect on growth (Hara et al. 1976). Based on these studies, the lowest-observed effect concentration (LOEC) values for iron are 28 and 50 mg/L, and the no-observed effect concentrations (NOECs) are 11.2 and 10 mg/L.”

Whole plant weight of common Oat (Avena sativa) was unaffected by exposure, under hydroponic cultivation conditions, to a concentration of 6.7 μM FeCl3 for 6 days following a 7-day period of cultivation under Fe-frree conditions. The results are difficult to interpret with respect to an exposure concentration in soil (Chen et al.1998).

The U.S. EPA (2003) Eco-SSL for Iron summarizes as follows: “Iron is essential for plant growth, and is generally considered to be a micronutrient. Iron is considered the key metal in energy transformations needed for syntheses and other life processes of the cells (Thompson & Troeh 1973). Consequently, plants regulate its uptake. In well aerated soils between pH 5 and 8, the iron demand of plants is higher than the amount available (Römheld & Marschner 1986). Because of this limitation, plants have evolved various mechanisms to enhance iron uptake (Marschner 1986). Under these soil conditions, iron is not expected to be toxic to plants.”

• Chen L, Dick WA, Streeter JG, Hoitink HAJ (1998). Fe Chelates from Compost Microorganisms Improve Fe Nutrition of Soybean and Oat. Plant Soil 200(2):139-47.
• Efroymson RA, Will ME, Suter II GW (1997a). Toxicological Benchmarks for Screening Contaminants of Potential Concern for Effects on Terrestrial Plants, 1997 Revision. ES/ER/TM-85/R3.
• Hara et al. (1976). CITATION LACKS IN SECONDARY SOURCE U.S. EPA 2003
• Marschner H (1986). Mineral nutrition of plants. Academic Press, New York.
• Mizuno N, Yoshida H (1993). Effect of Exchangeable Aluminium on the Reduction of Potato Scab. DOI: 10.1007/BF00025094 Plant and Soil 155-156(1):505-8 AND/OR In: Barrow N J (ed.). Plant Nutrition - from Genetic Engineering to Field Practice. Development in Plant Soil and Sciences. Kluwer Academic Publishers. Netherlands. p 751-4.
• Prasad J, Singh RS (1988). Effect of Potassium and Iron on Yields and Phosphorus, Calcium and Magnesium Content of Paddy (Oryza sativa L.). Agric Sci Dig 8(4):207-9.
• Römheld V, Marschner H (1986). Mobilization of iron in the rhizosphere of different plant species. In: Advances in Plant Nutrition, Volume 2, B. Tinker and A. Läuchli, eds. Praeger Scientific, New York, pp. 155-204.
• Singh V, Prakash O (1990). Effect of phosphorus and iron on yield and their content and uptake by wheat. Trans Indian Soc Desert Technol 15:63 -7.
• Subrahmanyam K, Nair AK, Singh DV (1991). Evaluation of diammonium and polyphosphates as carriers of iron and zinc in Japanese mint ratoon-mungbean cropping sequence. J Indian Soc Soil Sci 39(3):477-81.
• Thompson LM, Troeh FR (1973). Soils and Soil Fertility, 3rd edn McGraw-Hill Book Company.
• U.S. EPA United States Environmental Protection Agency (1993) Reregistration Eligibility Document (RED) Iron Salts / decision and fact sheet “R.E.D. FACTS “ Self-published, OPPTS (both document reference EPA-738-F-93-002). Self-published, Washington, DC, U.S.A.
• U.S. EPA United States Environmental Protection Agency (2003). Ecological Soil Screening Levels for Iron Interim Final OSWER Directive 9285.7-69. Self-published U.S. EPA, Office of Solid Waste and Emergency Response, Washington, DC, U.S.A. 44 p.
• Wallace A, Alexander GV, Chaudhry FM (1977(. Phytotoxicity and some interactions of the essential trace metals iron, manganese, molybdenum, zinc, copper, and boron. Commun Soil Sci Plant Ana. 8(9):741-50.
• Wallihan, E. F. 1966. Iron. In: Chapman, H. D. Diagnostic Criteria for Plants and Soils. University of California, Div. Agric. Sci., Riverside, CA, U.S.A. p 203-12.