LGC AXIO Proficiency Testing | Emerging Pollutants of Environmental Concern | Volume 1 | Neonicotinoids
Monitoring Strategy & Measurement of Neonicotinoids Five neonicotinoids (Imidacloprid, Clothianidin, Thiamethoxam, Acetamiprid and Thiacloprid) were included in the EU ‘Watch List’ of 17 chemicals in March 2015, which required each member state to monitor at least annually for a minimum number of monitoring sites. The UK monitoring of the EU Watch List was first carried out in 2016 for these five compounds, across 23 sites (16 in England, four in Scotland, and three in Wales), 17 were found to be contaminated with neonicotinoids, with 88% of samples taken found to contain one or more of the compounds of interest. The average detected neonicotinoid concentrations ranged from 0.002 to 0.443 µg/l. Eight of the monitored rivers in England exceeded recommended chronic pollution limits, and two were classified as acutely polluted. Surprisingly, Imidacloprid was detected in a number of arable river catchments despite it having very little use on arable fields in 2016 or the preceding few years [9]. Numerous authors in multiple countries have reported studies of neonicotinoid monitoring in surface waters over a number of years. A review of the literature for 29 studies, from nine countries found that neonicotinoids were detected in the majority of the water samples, irrespective of the water type; puddled water, irrigation channels, streams, rivers or wetlands [10]. The concentration data indicated an average surface water concentration of 0.13µg/L and a peak concentration, when the concentration increases dramatically during or shortly after the planting season, of 0.63µg/L. ____________________________________________ "A review of the literature for 29 studies, from nine countries found that neonicotinoids were detected in the majority of the waters sample, irrespective of the water type"
Environmental Fate
Neonicotinoids are water-soluble and break down slowly in the environment, properties which are key to their systemic mode of action as this enables them to be taken up by the plant and provide protection from insects as the plant grows. The degree of water solubility depends on the compounds themselves, the form of the application and the local conditions, such as ambient temperature and water pH. Water solubility means that any of the chemical which is not taken up by the plant may be a risk to the aquatic environment. The primary mechanism for transport of neonicotinoids into water bodies appears to be via rainfall run-off during or shortly after the planting season, though minor modes have been identified via direct contact with treated seeds, spray drift, leaching into groundwater and the decay of treated plant material [6]. Exposure of neonicotinoids to sunlight results in relatively rapid photodegradation; under natural light in rice paddies in Japan, imidacloprid was shown to have a half-life of 24.2 hours [7]. Under laboratory conditions researchers measured half-lives for five neonicotinoids under differing conditions to mimic the seasonal change found in Canada. They found 7-8- fold variations in the rate of neonicotinoid photolysis due to the variation in light levels across the season, results which are broadly similar to previously published studies with nitro-substituted neonicotinoid half-lives in the region of <1 – 3 days depending on light levels [8]. Neonicotinoids have been shown to have considerable persistence in soil; a review of available half-lives from field and laboratory studies conducted between 1999 and 2013 showed that reported half-lives are highly variable and typically range from 200 days to in excess of 1000 days for imidacloprid, 7–353 days for thiamethoxam and 148-6931 days for clothianidin. The half-lives of the nitro- substituted neonicotinoids appear to be shorter, at 3-74 days for thiacloprid and 31-450 days for acetamiprid. Half-lives of over 1 year would suggest the likelihood of neonicotinoid accumulation in the soil, assuming continuous input [5]. This potential for accumulation in the soil suggests the formation of a ‘bank of stored neonicotinoids’ and a constant source of exposure for soil dwelling organisms.
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