Obinna Nworie

Supervisor: Mike Wood

email: o.nworie@edu.salford.ac.uk

OVERVIEW:

Thesis title: Heavy metal dynamics in soil-plant system in contaminated soil in Greater Manchester, northwest England: Implications for management of heavy metal contaminated areas.

Thesis abstract: Soil–plant heavy metal transfer is a complex process controlled by natural and anthropogenic factors and represent a major pathway for human exposure to heavy metals. Understanding factors controlling metal dynamics in the soil-plant system is a vital knowledge gap which, when filled, will facilitate improved management of heavy metal contaminated areas.

Field, greenhouse and laboratory studies were conducted to investigate four aspects of this pathway: (a) mapping contamination levels across the study area (Moston Brook, Greater Manchester, UK) (b) assessing uptake by different herbaceous plant species, (c) monitoring seasonal dynamics in regrowth and uncut plant tissues, and (d) assessing the effects of compost and lime amendments on uptake by lettuce and mustard, and the associated health risks.

The study area was heavily contaminated by multiple heavy metals at levels above UK and EU tolerable limits. There was a poor relationship between most heavy metals and soil pH, EC and TOC. Historical anthropogenic industrial activity was the main controlling factor for soil heavy metal contamination. Heavy metal uptake by herbaceous plants was  affected by plant species, plant uptake capacity and soil characteristics. Several hyper-accumulating plants were identified. The plant tissue-borne heavy metals could affect microbial activities and consequently interfere with the ecosystem functioning. The signficant decrease in metal uptake in spring compared to the other seasons may be due to the dilution effect caused by increased plant biomass. The effects of compost and lime amendments were strongly dependent on vegetable species, amendment type and individual heavy metal.

The protocols developed in this research combining site assessment with assessment of uptake of herbaceous plant species, ex-situ monitoring of heavy metal accumulation and the use of amendments provide a framework that can be adapted in the global south for improved management of heavy metal contaminated areas and related  potential adverse effects on human health.