An initial field study conducted in 2020 by Martin and Hanson revealed that very low levels of herbicide can transfer to almonds during harvest operations, and those residues appear to be primarily due to herbicide-bound to soil particles. The European markets are integral to the economic success of the California almond industry; however, glyphosate and glufosinate are also very important to preharvest operations in the almond production system. The work presented here is a continuation of the project aimed to identify possible causes of low herbicide residues in almonds. The objectives of this project were to determine if low herbicide residues are still detectable in almonds throughout the process of commercial harvest operations and while the product moves through the huller/sheller processing facility.The preharvest herbicide treatment was applied on July 30, 2021. A tank mix of commercial glyphosate at 1,681 g ae ha-1 , growing racks commercial glufosinate at 1,681 g ai ha- 1 , nonionic surfactant at 0.25% v/v , and ammonium sulfate at 1% v/v . The herbicide was applied by the grower as part of regular commercial weed management using an unshielded boom sprayer. The application was made 26 days before the Nonpareil variety was shaken to the orchard floor and 48 days before the Aldrich variety was shaken. A table of all glyphosate and glufosinate applications made during the growing season is presented in Table 3.1.
The field location was divided into three replicates and three subsamples were taken within each replicate to form a composite sample from each variety. Leaves and almonds were sampled directly from both varieties of trees to help compare how much herbicide residue was present in the trees and on soil particles during and after harvest. Mature almond samples, including nuts with hulls, shells, and kernels, were taken from the windrow after undergoing the shaking and sweeping processes of harvest . Additionally, soil samples were taken at three important timepoints during the harvest process: before the preharvest herbicide treatment, before shaking, and from the windrow after sweeping . These three time points allowed for a snapshot of herbicide movement with soil particles. Both almond varieties were stockpiled at the huller sheller from the date of pick-up until the date of processing .Sampling at the huller/sheller took place on October 28, 2021 . Almonds that were sampled during this time were from the same 8-ha field location but did not correspond with the field replicate sampling, because nuts are bulked together during harvest. Sampling within the facility began after the system was full, or after the first kernels from the truckload reached the shipping bin. Two truckloads, containing about 50 metric tons of whole almonds each, took about 1.5 hours to go through the huller/sheller. The experimental almonds were processed to ship as shelled almonds; sampling occurred at the unloading, hulling, shelling, and shipment steps. First, composite samples were collected from the material stream as it left the truck hopper into the receiving pit of the facility.
Approximately 5 L of material was collected at the beginning, middle, and end of the truck unloading before the almonds entered the preprocess stage where sticks, rocks, excess soil, and other debris were removed using air, sieves, and gravity tables. Meanwhile, a soil sample was collected from the outlet where the fine debris exits the preprocessor at the same time points of the truck unloading. Then, while the batch of almonds was going through the hulling and shelling processes, hulls, shells, and kernels were sampled three times over 1.5 hours – at the beginning, middle, and end of the batch. Hulls were separated from the in shell almonds by gravity tables while shells were separated from kernels by gentle cracking and gravity tables. This sampling process was carried out for both Nonpareil and Aldrich varieties on the same day . Throughout this processing day, three soil samples were taken from the bag house, which collects the fine dust particles from multiple points in the hulling and shelling equipment, approximately 1.5 hours apart. Additional soil samples were collected directly from the hulling equipment and floor. All samples were brought to the laboratory and stored at room temperature until further hand processing and subsampling.Almond samples were further processed by hand and dissected into their hull, shell, and kernel fractions, soil samples were sifted using a 2 mm sieve, and leaf samples were dried. From the processed samples, a representative 500-gram sample was sent to a commercial laboratory for analysis. The laboratory used modified methods from QuPPe v 10 and high-pressure ion chromatography coupled with a mass spectrometer to quantify glyphosate, N-acetyl-glyphosate, AMPA, Nacetyl-AMPA, glufosinate, N-acetyl-glufosinate, and MPP in all almond samples. The soil samples were analyzed using the same instrumentation and modified methods from Druart et al. .
The limit of detection for each compound was 0.010 mg kg-1 for almonds samples and 0.040 mg kg-1 for soil samples.When examining the data presented it is worth noting that the field data are treated as a separate data set from the huller/sheller data because it was not possible to follow field replicates through the huller/sheller due to the harvest process resulting in the three replicates being stockpiled together; two truckloads from each stockpile were run through the processing facility. Soil sampling revealed quantities of parent compound and some metabolites at every stage of the experiment . Replicate 1 of the “Pre-Sweep” and “Post-Sweep” samples had very high concentrations of glyphosate and glufosinate parent compounds and metabolites. Replicate 1 is at the front of the field so it is suspected that the first subsample sample may have been contaminated by high levels of herbicide from initial equipment testing before the remainder of the field was sprayed, therefore, replicate 1 was not included in the analysis of those samples. There were no significant differences between or within any of the samples. The higher levels of herbicide from the bag house and the floor indicate there is detectable herbicide reside in particulate matter in the processing facility, but the filtration is doing its job by collecting those dust particulates in the baghouse. When comparing the soil data to the almond kernel data it is noteworthy that the major contributor to residues found in almonds is not the parent compound but the metabolites while the soil samples from the field and processing facility all contain detectable levels of parent compound, including the soil samples taken at the time of processing. Glyphosate was found in Aldrich leaf samples at an average concentration of 0.036 mg kg-1 , no glyphosate metabolites were detected. Nonpareil leaves were below the limit of detection of for glyphosate compounds. Glufosinate was found in two Aldrich leaf samples at an average concentration of 0.192 mg kg-1 . MPP was found in all Aldrich and Nonpareil leaf samples at an average concentration of 0.348 mg kg-1 . A summary of glyphosate residues found in almond fractions is presented in Table 3.6. Total glyphosate is presented as the sum of glyphosate, AMPA, N-acetyl-glyphosate, and Nacetyl-AMPA. Almond variety was not a significant factor in analysis so the Nonpareil and Aldrich data were pooled for a total of six replicate samples per sample location. The sample location was also not a significant factor in this field or huller/sheller data. There were no statistically significant differences between glyphosate concentrations in almond hulls and shells; the majority of kernel samples at all sampling stages were below the limit of detection. Glyphosate was not found in any kernels from the final processing step of the huller/sheller . AMPA and N-acetyl-AMPA were not found in any almond samples. Therefore, all kernel samples tested would be within the residue limits for total glyphosate within the US and glyphosate within the EU.
There were two kernel replicates with glyphosate compounds detected , growing weed vertically one was sampled from the truck and contained 0.010 mg kg-1 of glyphosate and the other was sampled directly from the tree and contained 0.012 mg kg-1 of N-acetyl-glyphosate. Both of these detections are at allowable concentrations as determined by the US and EU; additionally, the detection of glyphosate in these individual samples was below the ESFA proposed glyphosate MRL of 0.05 mg kg-1 . A summary of glufosinate residues found in almond fractions is presented in Table 3.5. Total glufosinate is presented as the summation of glufosinate, N-acetyl-glufosinate, and MPP. Almond variety was a significant factor in the data collected from the field but not in the data collected from the processing steps . Variety being a significant factor in glufosinate analysis is likely due to a physiological trait that is beyond the scope of this study. Both cultivars were grafted to the same peach rootstock, so differences in glufosinate concentration is likely not related to rootstock. The potential interaction between herbicide residue and rootstock and scion cultivars could be explored in future research. There were no significant differences between total glufosinate concentrations in hulls and shells at any sampling location or within the sampling locations. Sample location was also not a significant factor in total glufosinate concentrations in the Aldrich or Nonpareil kernels. Interestingly, total glufosinate concentrations in some Aldrich and Nonpareil kernel sampleswere above the EU MRL of 0.1 mg kg-1 , with the major contributor to the summation being MPP . The average concentration of MPP in Aldrich kernels coming from the huller/sheller, the last step of processing, was 0.89 mg kg-1 and the average concentration of MPP in the Nonpareils from the same sampling location was 0.109 mg kg-1 ; this is above the EU MRL for total glufosinate . However, the more surprising data came from the almonds sampled directly from the tree. Aldrich kernels from almonds sampled directly from the tree, having had no contact with the orchard floor, had an average MPP concentration of 0.76 mg kg-1 and the Nonpareil kernels had an average concentration of 0.104 mg kg-1 . A study conducted in apples of 14C-glufosinate-ammonium metabolism and translocation of soil applied chemical revealed that MPP did translocate from into fruits, leaves, and shoots 14 days after application . The study found concentration of MPP in apple fruits at 0.104 mg kg-1 , similar to the concentrations observed in almonds in this study; no parent compound was found in the apples. The previous study conducted by Martin and Hanson found MPP concentrations in almond kernels was roughly 0.05 mg kg-1 . These differences are suspected to be due to soil type differences between the 2020 site and the 2021 data in this paper and will be examined further in future studies. Almond hull, shell, and kernel residues were all below the United States MRLs for glyphosate, glufosinate, and their metabolites. However, the European Union MRLs total glufosinate in almond kernels were exceeded in Nonpareil kernels. Importantly, the concentration of MPP found in almond kernels sampled directly from the tree indicates that movement of the metabolite from the soil to the fruit may be playing a role in elevated residues before the almond touches the orchard floor. Throughout the growing season glufosinate was used consistently in the orchard , as is standard practice in many orchards. California growers will face challenges when choosing preharvest herbicide programs if the movement of glufosinate metabolites, specifically MPP, is proven to be a cause of herbicide residue in almonds, in addition to the pressures of potential MRL changes in the European Union. Future research in MPP residue levels in almonds before and after tree shake across California and across different soil types will help address domestic and export market concerns. Additionally, studies will continue to examine harvest operations for other sources of pesticide residues such as insecticides, fungicides, and other herbicides.The field of ecological restoration is growing rapidly in response to increasing human induced degradation of the Earth’s ecosystems .Despite this growth, there is still much to learn regarding how best to carry out ecosystem restoration . Realistic and tangible goal setting , scientifically supported restoration techniques , and novel theoretical frameworks have all been suggested as mechanisms to improve the success of restoration projects in achieving desirable outcomes. Rivers, creeks, and streams are often at the epicenter of restoration work . Along the West Coast of the United States, efforts to improve fish habitat, particularly for salmon, have directed significant restoration efforts towards these waterways . While dense human settlement near creeks may lead to their degradation, human proximity also facilitates connection with these natural spaces and interest in restoring the ecosystem.