Fate and effects of synthetic lubricants in soil: biodegradation and effect on crops in field studies

The production and use of synthetic, biodegradable lubricants has become increasingly widespread as a result of concern over the potential build-up in the environment of hydrocarbons derived from mineral oil-based lubricants. Due to the use of such lubricants in agricultural machinery, their fate and effects in soil have been investigated. A range of synthetic lubricants applied to field plots was found to degrade more rapidly and extensively than mineral oil-based lubricants, but not as rapidly or extensively as a natural vegetable oil. Loss of the oils was enhanced by the addition of nitrogen and the greatest losses were found in the warmer summer months. The extent and rate of biodegradation of the oils was much lower than that found previously in laboratory-based studies, but the relative biodegradabilities of the oils was consistent with previous results. At application rates of 5 l·m−2, both synthetic and mineral-based oils as well as the vegetable oil adversely affected the growth of spring wheat. However, the oils which caused the greatest effects were not necessarily the most persistent. Where sampling occurred over two growing seasons, the effect of residual oil was significantly reduced in the second season after oil application.