Progress and remaining challenges with the phase-out of methyl bromide under the Montreal Protocol

In response to global efforts by all countries under the Montreal Protocol since 1995, the phase-out of the major ozone-depleting gas, methyl bromide (MB), has been a significant success and benefit to the global environment. Since 1999, the reduction in MB production and use has led to a more than 30% reduction in the concentration of MB in the atmosphere and this has been responsible for more than 35% of the present fall in effective equivalent stratospheric chlorine (EESC) and a key chemical driver in the recovery of the ozone layer. The consequent impacts are reduced UV radiation, with flow on benefits to human health (fewer cancers and cataracts), agriculture (reduced crop damage) and improved durability of building materials, especially plastics. Since 1992, approx. 80% (60,000 t) of MB use worldwide has been phased-out, the majority being for pre-plant soil disinfestation uses to control soilborne pathogens and weeds. Only six 'critical uses' of MB remain in non-A5 (developed) and A5 (developing) countries beyond 2017. Four of these uses include pre-plant soil disinfestation in the strawberry nursery, strawberry fruit and tomato industries, and two uses for controlling pests in grain mills and houses. However, at present, quarantine and pre-shipment uses of MB (8500-10,000 t) are still exempt from phase-out. This includes pre-plant soil disinfestation in nursery industries in the USA and targeted applications for some soil quarantine pests (e.g., potato cyst nematode). Macrophomina phaseolina and some specific Fusarium spp. have reportedly increased in importance as pathogens in the strawberry fruit industry as a consequence of MB phase-out. Policy regulations are reducing the use and availability of the key chemical fumigant alternatives and this is forcing the world to consider more sustainable solutions for disease control, including shifting to soil-less culture production. Research focus globally for soil disinfestation to technologies which minimize pathogen populations and disease loss to sustainable levels, without the need for harsh chemical fumigation.