Plant, crop

Cannabis sativa L.

Industrial hemp

A fast-growing, deep-rooted fibre crop that tolerates metals. It stores them mainly in roots; its interest lies in producing non-food fibre on contaminated land. In Italy it has been grown for this purpose around the Taranto steelworks.

Thayne Tuason, CC BY-SA 4.0

How it works

Mechanisms: phytoextractionphytostabilisation

Contaminants

Contaminant	Evidence	What was shown
Cadmium	field	Field trial on metal-contaminated soil: extraction potential of 126 g Cd per hectare per growing season, with a check on fibre quality (Linger et al. 2002). In a two-year trial under Mediterranean climate hemp lowered extractable soil Cd by 32%, with no change in total content (Guidi Nissim et al. 2018). In semi-natural conditions Cd, Ni and Cr accumulate mainly in roots (Citterio et al. 2003). Linger et al., Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil: fibre quality and phytoremediation potential, Ind. Crops Prod. 16:33, 2002 Guidi Nissim et al., Trace element phytoextraction from contaminated soil: a case study under Mediterranean climate, Environ. Sci. Pollut. Res. 25:9114, 2018 Citterio et al., Heavy metal tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L., Plant Soil 256:243, boa.unimib.it, 2003
Lead	field	In the Mediterranean trial hemp gave the best lead extraction rate of the four species compared (36 g/ha/year) and lowered extractable Pb by 46% (Guidi Nissim et al. 2018). On a Belgian site contaminated with Cd, Pb and Zn stem yield fell 30–50% against the control (De Vos et al. 2023). Guidi Nissim et al., Environ. Sci. Pollut. Res. 25:9114, 2018 De Vos et al., Industrial hemp (Cannabis sativa L.) field cultivation in a phytoattenuation strategy and valorization potential of the fibers for textile production, Environ. Sci. Pollut. Res. 30:41665, 2023

Contaminant

Evidence

What was shown

Cadmium

field

Field trial on metal-contaminated soil: extraction potential of 126 g Cd per hectare per growing season, with a check on fibre quality (Linger et al. 2002). In a two-year trial under Mediterranean climate hemp lowered extractable soil Cd by 32%, with no change in total content (Guidi Nissim et al. 2018). In semi-natural conditions Cd, Ni and Cr accumulate mainly in roots (Citterio et al. 2003).

Lead

field

In the Mediterranean trial hemp gave the best lead extraction rate of the four species compared (36 g/ha/year) and lowered extractable Pb by 46% (Guidi Nissim et al. 2018). On a Belgian site contaminated with Cd, Pb and Zn stem yield fell 30–50% against the control (De Vos et al. 2023).

Limits

The amounts extracted are small (tens to a few hundred grams per hectare per year) and total soil content does not change within a few years. At Taranto the C.A.N.A.P.A. project grew hemp on farmland near the ILVA plant; the available report is a conference paper and its authors state that longer trials are needed for definitive data on metals, dioxins and PCBs (Colao et al. 2015). For dioxins and PCBs the sources consulted contain no removal measurements. Fibre must be tested before use.

Where it has been tried

Former Loring Air Force Base (Mi'kmaq Nation land)

PhytoremediationField scale, 2022

Cannabis sativa

The Mi'kmaq Nation, the Upland Grassroots group and researchers from several institutions (Nason, White and colleagues) grew hemp in the field and analysed PFAS in paired plant and soil samples; the harvested hemp was treated by hydrothermal liquefaction to destroy the PFAS.

Outcome Hemp took up 10 of the 28 PFAS, carboxylic acids and short-chain compounds best. In all it removed about 1.4 mg of PFAS, at most some 2% of what the soil held in the best area. The authors write that hemp is not at present a comprehensive solution for PFAS-contaminated soil. Liquefaction degraded nearly 100% of the carboxylic acids; part of the sulfonic acids remained.

Per- and polyfluoroalkyl substances

Nason et al., A comprehensive trial on PFAS remediation: hemp phytoextraction and PFAS degradation in harvested plants, Environmental Science: Advances, pmc.ncbi.nlm.nih.gov, 2024

Taranto

PhytoremediationField scale, 2014–

Cannabis sativa

Vincenzo Fornaro, with the CanaPuglia association, sowed hemp in April 2014 on the land where the sheep used to graze, to convert the farm (fibre, products) and with the stated aim of cleaning the soil. A second phase, funded by the regional «Principi Attivi» call, was to sample the plants.

Outcome No measured result was found: the sources consulted are press articles and report no soil or plant analyses. The remediation effect of hemp at Taranto therefore remains undocumented.