Plant, grass

Festuca arundinacea Schreb.

Tall fescue

A robust perennial grass, tolerant of hydrocarbons and creosote, with roots that are dense and deep for a grass. It is the plant of combined systems in which tillage, degrading bacteria and growth-promoting rhizobacteria work together.

Forest & Kim Starr, CC BY 3.0

How it works

Mechanisms: rhizodegradation

Contaminants

Contaminant	Evidence	What was shown
Petroleum hydrocarbons	field	A 270-day field trial on 2,000 m² at a hydrocarbon-contaminated site in northern Italy, with F. arundinacea, Dactylis glomerata, alfalfa and bird's-foot trefoil, native bacteria and mycorrhizae: the authors report remarkable remediation potential for both grasses and legumes, with soil enzyme activities rising along with degradation (Zuzolo et al. 2020). From the research group behind the multi-process system, a three-year test in Ontario on a land farm for refinery waste brought total hydrocarbons from 130 to about 50 g/kg (Gurska et al. 2009; the abstract does not list the species). Zuzolo et al., Plant-soil-microbiota combination for the removal of total petroleum hydrocarbons (TPH): an in-field experiment, Front. Microbiol. 11:621581, 2020 Gurska et al., Three year field test of a plant growth promoting rhizobacteria enhanced phytoremediation system at a land farm for treatment of hydrocarbon waste, Environ. Sci. Technol. 43:4472, 2009
Creosote	greenhouse	Multi-process system on creosote soil (tillage, degrading bacteria, growth-promoting rhizobacteria and tall fescue): over four months average removal of the 16 priority PAHs was twice that of land-farming alone, 50% more than bioremediation alone and 45% more than phytoremediation alone, including the most hydrophobic PAHs (Huang et al. 2004). Huang et al., A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soils, Environ. Pollut. 130:465, 2004

Contaminant

Evidence

What was shown

Petroleum hydrocarbons

field

A 270-day field trial on 2,000 m² at a hydrocarbon-contaminated site in northern Italy, with F. arundinacea, Dactylis glomerata, alfalfa and bird's-foot trefoil, native bacteria and mycorrhizae: the authors report remarkable remediation potential for both grasses and legumes, with soil enzyme activities rising along with degradation (Zuzolo et al. 2020). From the research group behind the multi-process system, a three-year test in Ontario on a land farm for refinery waste brought total hydrocarbons from 130 to about 50 g/kg (Gurska et al. 2009; the abstract does not list the species).

Creosote

greenhouse

Multi-process system on creosote soil (tillage, degrading bacteria, growth-promoting rhizobacteria and tall fescue): over four months average removal of the 16 priority PAHs was twice that of land-farming alone, 50% more than bioremediation alone and 45% more than phytoremediation alone, including the most hydrophobic PAHs (Huang et al. 2004).

Huang et al., A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soils, Environ. Pollut. 130:465, 2004

Limits

Alone the plant does less than the combined system: the result depends on tillage and inocula. It acts in the root layer. After three years in Ontario about 50 g/kg of hydrocarbons remained: a large reduction, not a complete clean-up. Many varieties host an endophytic fungus toxic to livestock, and forage from a contaminated site should not be used anyway.

Where it has been tried

Brescia-Caffaro

PhytoremediationGreenhouse, with soil from the site

Festuca arundinacea, Cucurbita pepo subsp. pepo, Medicago sativa, Phalaris arundinacea

Greenhouse rhizoremediation trial on farm soil from the SIN contaminated with aged PCBs (mg/kg range), in 6 kg pots to approach field conditions. Ten treatments in triplicate: seven species (grasses and trees) and five growing conditions (single species, intercropping, redox cycle by flooding, added compost or ammonium thiosulfate), with unplanted controls, for 18 months. The same experiment produced soil half-lives for PCBs and for dioxins and furans.

Outcome After 18 months total PCBs had fallen by 14–20%. The best treatments (about 20%) were Festuca arundinacea with compost, Festuca arundinacea grown with Cucurbita pepo, and Medicago sativa with Rhizobium and mycorrhizal fungi. PCB half-lives ranged from 1.3 to 5.6 years. For dioxins and furans only Festuca arundinacea gave a significant reduction (11–24% depending on the congener; half-lives 2.5–5.8 years). In a later column test, soil grown with Medicago sativa released about twice as much PCB in leachate, bound to particulate organic carbon.

PhytoremediationGreenhouse, with soil from the site, 2015–2016

Festuca arundinacea, Phalaris arundinacea, Cucurbita pepo subsp. pepo, Medicago sativa, Brassica juncea, Salix caprea, Athyrium filix-femina

The University of Insubria, the University of Milan and ERSAF took about 2,500 kg of soil from the site and grew plants on it in a greenhouse for 18 months (May 2015 – November 2016) in 6 kg pots: ten treatments in triplicate with seven species, intercropping, compost, redox cycles and ammonium thiosulphate, with unplanted controls. It is a semi-field trial, not an open-field one.

Outcome After 18 months total PCBs had fallen by 14–20%. The best treatments (Festuca arundinacea with compost or intercropped with pumpkin; alfalfa with Rhizobium and mycorrhizal fungi) reached about 20%. For dioxins and furans tall fescue alone gave reductions of 11–24% depending on the congener, with half-lives of 2.5–5.8 years. The authors name the short duration, against the persistence of these compounds, as a limit.