Abstract
The forested regions of Northern California, while not an area of intense agricultural activity, has its own unique pesticide applications. Unregulated Cannabis cultivators apply unknown types and quantities of pesticides, including substances banned in the United States. In addition, pesticides are used in commercial timber production. These chemicals may be entering streams at concentrations harmful to aquatic animals and plants. This study utilized passive sampling devices called Chemcatchers® to sample surface waters downstream from Cannabis and timber production sites. Passive sampling can catch pollutant pulses that may be missed by traditional grab sampling. Trace levels of pesticides can be concentrated in passive sampler media to detectable levels without requiring large volumes of water to be collected, which is especially useful when sampling more remote locations. These attributes make passive sampling an attractive technique for areas that receive seasonal or episodic pesticide loads. Samplers containing Atlantic® HLB and Empore™ SDB-RPS sorbent disks with and without diffusion limiting membranes were deployed in the fall of 2016 and summer 2017. This study includes method development, laboratory spiking experiment, field comparison study, and an environmental field study. Overall, the laboratory spike test yielded acceptable recoveries for both disk types (percent recovery 50-130%) for 90% of the 168 total analytes assessed in this experiment, a total of 152 chemicals. Field comparison of the disk types suggested the Empore™SDB-RPS performed better in the field than the Atlantic® HLB with a frequency of detection of 80% the total detections as configured in this study. In the field comparison study, twenty-seven pesticides were detected in total; of the 27 pesticides 6 were detected using the HLB, 24 were detected using the SDB-RPS, and 3 by grab sampling. Eight different pesticides were detected downstream from timber and Cannabis cultivation areas. The analytes detected included the herbicides dacthal (DCPA), dithiopyr, hexazinone, and trifluralin. Also detected was the insecticide degradate p,p’-DDE and the fungicides chlorothalonil, imazalil, and thiabendazole. Concentrations ranged from 5 to 46 ng/disk.