1) Search terms ‘x+tolerance+field trial’ were used where ‘x’ is As, Cd, Hg or Zn respectively. Within the search output, papers were included that were based on one or more of the following strategies: ‘Metal(loid) liganding and vacuolar sequestration’; ‘Alteration of transport’; ‘Changes in root morphology/architecture’; or ‘Effects on plant tolerance of plant-growth-promoting rhizobacteria/fungi’.