hydronium;iron(3+);hexahydroxide;disulfate

Bioaccumulation: terrestrial

Description of key information

The available information indicates no concerns with regard to enrichment in air breathing biota.

Additional information

This endpoint is covered by the category approach for dissociating, inorganic and non-toxic iron compounds (please see the section on physical and chemical properties for the category justification/report format). Iron as an essential trace element is well regulated in biota. Differences in uptake rates are therefore likely to be related to essential needs varying with the species, size, life stage, seasons etc. rather than indication bioaccumulation. Where there is a deficiency, iron additions would be beneficial up to a limiting value. Testing is complicated by speciation such as the rapid conversion of iron salts to insoluble iron hydroxides. Nonetheless some information is available from the literature.

A paper by Motalib et al (1997) shows that there is no relationship between soil iron levels and earthworm tissue bioconcentrations, indicating that iron uptake is low.

The growth and bioaccumulation of five elements (cadmium, copper, iron, lead and zinc) in earthworms (Lumbricus terrestris) from unfortified soils was investigated by Rida (1996). Bioaccumulation was related to the duration of exposure, tested element, and physiological condition (i.e. adult or cocoon) of the earthworms. The potential synergistic or antagonistic effects related to the geochemistry of the tested elements were not evaluated.

Beyer & Stafford (1993) measured iron concentrations in soils and earthworms from 18 sites at nine confined dredge disposal facilities in the Great Lakes Region, USA. A minimum of 38 g of earthworms was collected per site and earthworms’ digestive tracts were not purged, because wildlife would ingest that soil with their prey. For each of the 18 sites a BAF value was calculated based on the measured soil and earthworms iron concentrations. An overall median BAF value for the 18 sites of 0.38 can then be calculated. No overall iron bioaccumulation had been observed

Differences in iron concentrations among terrestrial species seem likely to be not related to the level in the trophic chain but to the capability of internal homeostasis and elimination.

Głowacka et al (1997) determined iron concentrations in 14 species of psyllids and in leaves of their host plants from unpolluted sites in Finland and two industrially polluted sites in Poland. Psyllids may play a double role in metal transfer, by producing metalcontaminated honeydew and as potential prey, mainly for ants. Metal burdens in psyllids were generally low. The average levels of iron in insects from contaminated sites in Poland (367.3 and 435.4 mg/kg dry weight) were significantly higher when compared with the data for psyllids from unpolluted sites in Finland (273.2 mg/kg dry weight). The biomagnification of metals in psyllids was species and metal dependent, even in those species which utilized the same host plant. The average biomagnification factor for iron in the 14 species was 1.8 indicating little or no biomagnification. Excretion of metals with honeydew was efficient for elimination of aluminium, iron, zinc and nickel in Ps. fraxini from a polluted site, but was generally low in species from unpolluted sites. The ratio of metal concentrations in honeydew against metal contents in leaves was generally lower than unity, which demonstrates absence of bioaccumulation via honeydew secretion.

The available evidence gives no evidence for iron biomagnification across the terrestrial tropic chains.

• Głowacka E, Migula P, Nuorteva S, Tulisalo E (1997). Psyllids as a Potential Source of Heavy Metals for Predators. Arch Environ Contam Toxicol 32:376–82.
• Motalib A, Abdul Rida M, Bouche MB (1997). Heavy Metal Linkages with Mineral, Organic and Living Soil Compartments. Soil Biol Biochem 29(3/4):649-55.
• Rida AM (1996). Growth and trace element concentration in the earthworm and plants in non-contaminated soils and soil contaminated with cadmium, copper, iron, lead, and tin: Soil-earthworm interactions. Soil Biol. Biochem. 28(8):1029-35.