Several classes of
pesticides have been shown to impair water quality in California, including
organophosphates, pyrethroids and neonicotinoids. Vegetative treatment systems (VTS) can reduce
pesticide loads and associated toxicity in agricultural runoff, but many
water soluble pesticides such as neonicotinoids are not effectively treated by
VTS, and VTS installation is not always an option for growers required to
remove non-crop vegetation for food safety concerns. Recent studies have shown that biochar
filtration can be used to remove soluble contaminants, especially when coupled
with other VTS components. We evaluated
a mobile carbon filter system consisting of a trailer-mounted tank containing approximately
600L (~180 kg) of biochar. Input water
from a 437 hectare agricultural drainage was pre-filtered and treated with
biochar during two multi-week study periods.
Laboratory toxicity tests and chemical and nutrient analyses were
conducted on input and output water.
Pesticide concentrations were initially reduced by greater than 99%. Treatment efficacy declined linearly and was
expected to remain at least 50% effective for up to 34 weeks. Toxicity was assessed with Ceriodaphnia dubia, Hyalella azteca and Chironomus
dilutus. Significant input toxicity
was reduced to non-toxic levels in 6 of 16 samples. Some input concentrations of the
neonicotinoid imidacloprid and the pyrethroid cypermethrin exceeded
organism-specific toxicity thresholds and benchmarks, but the overall causes of
toxicity were complex mixtures of agricultural chemicals. Nutrients were not reduced by the
biochar. Results demonstrate the utility
of biochar in treating agricultural runoff and provide measures of the
longevity of biochar under field conditions.
