An Ecological Risk Assessment of the Acute and Chronic Toxicity of the Herbicide Picloram to the Threatened Bull Trout (Salvelinus confluentus) and the Rainbow Trout (Onchorhyncus mykiss)

Abstract

We conducted acute and chronic toxicity studies of the effects of picloram acid on the threatened bull trout (Salvelinus confluentus) and the standard coldwater surrogate rainbow trout (Oncorhynchus mykiss). Juvenile fish were chronically exposed for 30 days in a proportional flow-through diluter to measured concentrations of 0, 0.30, 0.60, 1.18, 2.37, and 4.75 mg/L picloram. No mortality of either species was observed at the highest concentration. Bull trout were twofold more sensitive to picloram (30-day maximum acceptable toxic concentration of 0.80 mg/L) compared to rainbow trout (30-day maximum acceptable toxic concentration of 1.67 mg/L) based on the endpoint of growth. Picloram was acutely toxic to rainbow trout at 36 mg/L (96-h ALC50). The acute:chronic ratio for rainbow trout exposed to picloram was 22. The chronic toxicity of picloram was compared to modeled and measured environmental exposure concentrations (EECs) using a four-tiered system. The Tier 1, worst-case exposure estimate, based on a direct application of the current maximum use rate (1.1 kg/ha picloram) to a standardized aquatic ecosystem (water body of 1-ha area and 1-m depth), resulted in an EEC of 0.73 mg/L picloram and chronic risk quotients of 0.91 and 0.44 for bull trout and rainbow trout, respectively. Higher-tiered exposure estimates reduced chronic risk quotients 10-fold. Results of this study indicate that picloram, if properly applied according to the manufacturer's label, poses little risk to the threatened bull trout or rainbow trout in northwestern rangeland environments on either an acute or a chronic basis.

Theoretical studies on the kinetics and mechanism of hydroxyl radical reaction with quinclorac and quinmerac herbicides in aqueous media

“…This augments their availability for its degradation processes. Various types of degradation processes are applied for these herbicides which are mainly based on biological degradation methods [10–16], chemical methods [17, 18] and photodecomposition methods [19–23]. In many instances, it has been observed that a combination of chemical method with photocatalysis is also used widely and considered as the most effective oxidative degradation process [24].…”

Chemically engineered unzipped multiwalled carbon nanotube and rGO nanohybrid for ultrasensitive picloram detection in rice water and soil samples

“…Its half-life in the soil is reported to be in the range of 1 to 13 months based on certain circumstances 7 . At a concentration of 470 g/mL, it can easily seep into the soil and groundwater by virtue of agricultural usage and elimination of inappropriate wastes 8 , 9 thus damaging adjacent non-target species of crops from purified ones and posing a hazardous danger to aquatic species 10 – 12 . Recent research has identified picloram as an ecological hormone of low toxicity but high carcinogenicity 13 .…”

Determination of genotoxic damages of picloram and dicamba with comet assay in Allium cepa rooted in tissue culture and distilled water

“…Picloram usage comes after glyphosate, throughout the world [4]. This auxin herbicide is commonly used to kill dicotyledonous weeds in crop elds and pastures [5]. According to the data described in the EPA (1995) report, Picloram does not cause chromosomal damage; declared non-toxic at low doses to birds, mammals, and aquatic species.…”