Arbuscular mycorrhizas amplify the risk of heavy metal transfer to human food chain from fly ash ameliorated agricultural soils.

Soil contaminants threaten global food security by posing threats to food safety through food chain pollution. Fly ash is a potential agent of soil contamination that contains heavy metals and hazardous pollutants. However, being rich in macro- and micronutrients that have direct beneficial effects on plant growth, fly ash has been recommended as a low-cost soil ameliorant in agriculture in countries of the Global South. Arbuscular mycorrhizal fungi (AMF), ubiquitous in agricultural soils, enhance efficiency of plant nutrient uptake from soils but can equally increase uptake of toxic pollutants from fly ash ameliorated soils to edible crop tissues. We investigated AMF-mediated amplification of nutrient and heavy metal uptake from fly ash amended soils to shoots, roots and grains of barley. We used a microcosm-based experiment to analyse the impacts of fly ash amendments to soil in concentrations of 0 (control), 15, 30 or 50% respectively, on root colonization by AMF Rhizophagus irregularis and AMF-mediated transfer of N, P and heavy metals: Ni, Co, Pb and Cr to barley tissues. These concentrations of fly ash are equivalent to 0, 137, 275 and 458 t ha-1 respectively, in soil. Root AMF colonization correlated negatively with fly ash concentration and was not detected at 50% fly ash amendment. Shoots, roots and grains of mycorrhizal barley grown with 15, 30 and 50% fly ash amendments had significantly higher concentrations of Ni, Co, Pb and Cr compared to the control and their respective non-mycorrhizal counterparts. Presence of heavy metals in barley plants grown with fly ash amended soil and their increased AMF-mediated translocation to edible grains may significantly enhance the volume of heavy metals entering the human food chain. We recommend careful assessment of manipulation of agricultural soils with fly ash as heavy metal accumulation in agricultural soils and human tissues may cause irreversible damage.

Arbuscular mycorrhizas accelerate the degradation of colour containing organic pollutants present in distillery spent wash leachates.

Distillery spent wash (DSW) from molasses-based distilleries is being used as a low-cost alternative to chemical fertilizers in countries like India and Brazil. However, using DSW as a fertilizer substitute causes organic pollutant leaching, including melanoidins and caramel colourants that turn bodies of water dark brown. This study investigated the arbuscular mycorrhiza (AM) mediated degradation of organic pollutants in DSW. Mycorrhizal and non-mycorrhizal Sorghum bicolor were grown in microcosms for 16 weeks. The plants were fertilized with either raw DSW or Hoagland solution. Leachates draining from the microcosms after fertilization were collected three times in 30-day intervals. Each 30-day collection was preceded by two fertilizations. A gas chromatography-mass spectrometry comparative analyses of raw DSW with leachates of the third collection from mycorrhizal and non-mycorrhizal microcosms was made. Sixty-five and 42 complex organic compounds were detected in raw DSW and leachate collected from the non-mycorrhizal pots respectively. Only 26 compounds were detected in leachate collected from mycorrhizal pots. Absent from leachate of the mycorrhizal pots were: colour-containing organic compounds diacetone alcohol; 3-amino-2-cyano-6-methyl-6,7-dihydrothieno[2,3-b]pyrazine S-oxide; cyclohexane; 1,2-benzenedicarboxylic acid, butyl 8-methylnonyl ester; 2-pyrrolidinone; and acetic acid, dodecyl ester present in raw DSW. The results indicate that AM fungi can degrade organic pollutants in DSW.