Soil sterilants are non-selective residual herbicides that render the treated soil unfit for plant growth for relatively long periods of time. Sterilants were commonly used in Alberta from the 1960s to late 1990s for non-selective vegetation control on oil and gas wells, gas processing plants, rights-of-way, railways, saw mills, pulp mills, and electrical utility sites; residues may also be found at agrochemical dealer sites. Sterilant treated areas can remain devoid of vegetation for many years, depending upon the type, rate and frequency of application of soil sterilant and the climatic conditions. Soils treated with sterilant can be a source of contamination through leaching, surface runoff and wind dispersion of the sterilants to adjacent land and waterbodies. Reclamation and remediation issues arise when a treated site is no longer needed for industrial use and the site must be returned to equivalent land capability. At present, many of these sites either remain as liabilities for industry, or impacted soil is excavated and disposed at a landfill.
This review identified that a considerable body of knowledge exists regarding residual herbicide properties and their use in agricultural settings at low rates; however, limited knowledge is available on industrial uses, and in particular, on field-scale remediation of sites affected by the sterilants historically used in Alberta. Several major challenges were identified associated with management of sterilant impacted sites in Alberta through this literature review, industry consultation and personal communication, including 1) the research and demonstration trials that have been undertaken have limited applicability to Alberta conditions and/or have mostly been done in the laboratory or greenhouse, 2) information on the effects of sterilants on Alberta-specific native plants is very limited, and 3) the majority of remediation information found in the literature focuses on soils rather than surface water or groundwater which is a significant problem for Alberta sites where highly mobile sterilants such as bromacil have been used.
There are considerable differences between sterilants in terms of persistence and fate in the environment which depend on several factors related to the sterilant itself and to the soil and climatic conditions, resulting in unique challenges associated with each of them. The two main sterilants found impacting soil and groundwater on or near industrial sites in Alberta include bromacil and tebuthiuron. Several technologies have been utilized to treat sterilant-contaminated soils, both in-situ and ex-situ. The most common treatment technique previously used in Alberta has been sterilant-immobilization, utilizing activated carbon, however several gaps were identified with utilizing this technique for long term management of sterilant impacted sites. Additional knowledge gaps were identified related to the effective management of sterilant impacted sites in Alberta (and have been substantiated through conversations with Alberta practitioners in recent workshops sponsored by InnoTech Alberta).