Allan S. Felsot

Agrochemical spray drift; assessment and mitigation—A review*

During application of agrochemicals spray droplets can drift beyond the intended target to non-target receptors, including water, plants and animals. Factors affecting this spray drift include mode of application, droplet size, which can be modified by the nozzle types, formulation adjuvants, wind direction, wind speed, air stability, relative humidity, temperature and height of released spray relative to the crop canopy. The rate of fall of spray droplets depends upon the size of the droplets but is modified by entrainment in a mobile air mass and is also influenced by the rate of evaporation of the liquid constituting the aerosol. The longer the aerosol remains in the air before falling to the ground (or alternatively striking an object above ground) the greater the opportunity for it to be carried away from its intended target. In general, all size classes of droplets are capable of movement off target, but the smallest are likely to move the farthest before depositing on the ground or a non-target receptor. It is not possible to avoid spray drift completely but it can be minimized by using best-management practices. These include using appropriate nozzle types, shields, spray pressure, volumes per area sprayed, tractor speed and only spraying when climatic conditions are suitable. Field layout can also influence spray drift, whilst crop-free and spray-free buffer zones and windbreak crops can also have a mitigating effect. Various models are available to estimate the environmental exposure from spray drift at the time of application.

Disposal and Degradation of Pesticide Waste

Generation of pesticide waste is inevitable during every agricultural operation from storage to use and equipment cleanup. Large-scale pesticide manufacturers can afford sophisticated recovery, treatment, and cleanup techniques. Small-scale pesticide users, for example, single farms or small application businesses, struggle with both past waste problems, including contaminated soils, and disposal of unused product and equipment rinsewater. Many of these problems have arisen as a result of inability to properly handle spills during, equipment loading and rinsewater generated after application. Small-scale facilities also face continued problems of wastewater handling. Old, obsolete pesticide stocks are a vexing problem in numerous developing countries. Pesticide waste is characterized by high concentrations of a diversity of chemicals and associated adjuvants. Dissipation of chemicals at elevated concentrations is much slower than at lower concentrations, in part because of microbial toxicity and mass transfer limitations. High concentrations of pesticides may also move faster to lower soil depths, especially when pore water becomes saturated wish a compound. Thus, if pesticide waste is not properly disposed of, groundwater and surface water contamination become probable. The Waste Management Hierarchy developed as an Australian Code of Practice can serve as a guide for development of a sound waste management plan. In order of desirability, the course of actions include waste avoidance, waste reduction, waste recycling, waste treatment, and waste disposal. Proper management of pesticide stocks, including adequate storage conditions, good inventory practices, and regular turnover of products,. will contribute to waste avoidance and reduction over the long-term. Farmers can also choose to use registered materials that have the lowest recommended application rates or are applied in the least volume of water. Wastewater that is generated during equipment rinsing can be recycled by spraying it onto cropland, thus avoiding a soil contamination problem. If it is not feasible to spray out rinsates, then water treatment becomes necessary. However, for small waste generators, practical technology is still too experimental and not easily implemented on an individual farm or at a small application business. Nevertheless, research has been quite active in application of advanced oxidation processes (UV/ozonation: photoassisted Fenton reaction: photocatalysis using TiO2). Obsolete pesticide stocks in developing countries are being packaged and shipped to developed countries for incineration. Contaminated soil can also be incinerated, but this is not practical nor affordable for small waste generators. Chemical degradation of chlorinated hydrocarbon pesticides may be amenable to dechlorination by alkali polyethylene glycol treatment, but further study is needed to make the technique practical for small waste generators. Contaminated soils may be amenable to cleanup by one of several biological treatment methods, including composting, landfarming, and bioaugmentation/ biostimulation. Composting and landfarming (which may be used in combination with biostimulation) may be the most practical of the biological methods that is immediately ready for implementation by small-scale pesticide waste generators.

Adsorption of carbofuran and movement on soil thin layers

Carbofuran is a widely used soil insecticide throughout the Midwest as a prophylactic treatment against corn rootworms. In Iowa and Illinois alone, approximately 3.5 million pounds of active ingredient were applied to the soil in 1979. 1 Since treated fields occur in both watershed and nonwatershed areas alike, it is desirable to describe the translocation potential of this insecticide. HELLING (1968) devised a mobility classification for agricultural chemicals based upon their movement on soil thin layers. Since carbofuran mobility has not been assessed by soil TLC, the objective of this study was to determine its movement using this method. Adsorption of carbofuran was also measured to elucidate the relationship between sorption and translocation.

Options for cleanup and disposal of pesticide wastes generated on a small-scale

Abstract Many processes have been investigated to dispose of obsolete pesticide stocks and clean up wastewater and contaminated soil. The processes vary in their stages of development and commercial utility. With the exception of incineration, no single process may be amenable to all pesticide waste. Thus, any chosen process must consider first the chemical constituents needing remediation, their concentration, and desired or regulated cleanup objectives. Incineration seems too impractical and expensive to clean up routinely generated wastewater and contaminated soil, but it may currently be the only practical option for obsolete stocks . Practical remediation processes for wastewater and contaminated soil produced by small waste generators are discussed. Cleanup should be viewed as an integration of physical, chemical, and biological technologies.

Environmental chemodynamic studies with terbufos (counter®) insecticide in soil under laboratory and field conditions

The effect of temperature, soil moisture, soil type, adsorption, and formulation on terbufos persistence in soil was studied under laboratory conditions. Temperature appeared to be more important than moisture in influencing the dissipation rate of terbufos. More terbufos was recovered from a granular formulation than a technical formulation one month after incubation. Soil adsorption coefficient and calculated first order rate constant were well correlated. Terbufos was relatively immobile on soil thin layers and in field-located soil columns. Laboratory data agreed reasonably well with measurements of persistence in the field. Terbufos degradation kinetics were qualitatively analyzed and the toxicological significance of studying parent terbufos alone was discussed.

Survey and Risk Assessment of Apis mellifera (Hymenoptera: Apidae) Exposure to Neonicotinoid Pesticides in Urban, Rural, and Agricultural Settings.

Abstract A comparative assessment of apiaries in urban, rural, and agricultural areas was undertaken in 2013 and 2014 to examine potential honey bee colony exposure to neonicotinoid insecticides from pollen foraging. Apiaries ranged in size from one to hundreds of honey bee colonies, and included those operated by commercial, sideline (semicommercial), and hobbyist beekeepers. Residues in and on wax and beebread (stored pollen in the hive) were evaluated for the nitro-substituted neonicotinoid insecticides imidacloprid and its olefin metabolite and the active ingredients clothianidin, thiamethoxam, and dinotefuran. Beebread and comb wax collected from hives in agricultural landscapes were more likely to have detectable residues of thiamethoxam and clothianidin than that collected from hives in rural or urban areas (∼50% of samples vs. <10%). The maximum neonicotinoid residue detected in either wax or beebread was 3.9 ppb imidacloprid. A probabilistic risk assessment was conducted on the residues recovered from beebread in apiaries located in commercial, urban, and rural landscapes. The calculated risk quotient based on a dietary no observable adverse effect concentration (NOAEC) suggested low potential for negative effects on bee behavior or colony health.

Leaf photosynthesis, stomatal resistance, and growth of wine grapes (Vitis vinifera L.) after exposure to simulated chlorsulfuron drift

Abstract The lower Yakima Valley of Washington is a highly diversified irrigated agricultural region bordered by dryland wheat fields. Residues of herbicides sprayed in wheat can be atmospherically transported to susceptible nontarget crops in the valley. Nontarget crops may be exposed repeatedly to low levels of herbicide residues. The effects on grapes exposed to phenoxyacetate herbicide drift has been well documented, but the effects of comparatively newer wheat herbicides like sulfonylureas (SUs) are less known. Potential effects of repeated exposures of grapes to an SU herbicide were assessed in a simulated drift study. Grape vines of the cultivar “Lemberger”; were sprayed up to three times at a weekly interval with 1/100 (0.01X) of a field application rate of chlorsulfuron, which is a postemergence wheat herbicide. Thirty‐five days after the first application, photosynthesis and stomatal resistance of randomly tagged, fully expanded leaves were measured. Total leaf area and chlorotic leaf area were ...

Bioremediating herbicide-contaminated soils

Combinations of landfarming and biostimulation were evaluated for remediating pesticide wastes. Various amounts of soil contaminated with alachlor and trifluralin (≥100 mg/kg each) and metolachlor and atrazine (≥20 mg/kg each) were applied to field plots, and sewage sludge or corn meal was incorporated into designated plots. Plots were also treated with fresh spray mixtures in amounts similar to those applied as contaminated soil. Soil bioactivity and dissipation of parent herbicides were monitored after the treatments. During 100 d, soil dehydrogenase activities were highest in organic-material-amended plots. During the same period, the levels of alachlor had declined by 85–95% in amended, contaminated soil-treated plots and by 75–85% in corresponding unamended plots. In freshly sprayed plots, 95–100% of the initial doses of alachlor had dissipated in amended plots, and 85–95% was lost in corresponding unamended plots. The levels of trifluralin had declined by 70–80% in corn-meal-amended plots and by 60–75% in unamended plots. There were no significant differences between dissipation of trifluralin applied as contaminated soil or fresh sprays.

Effects of conditioning, cross-conditioning, and microbial growth on development of enhanced biodegradation of insecticides in soil

Abstract Pretreatment of a Drummer‐Catlin soil mixture with granular formulations of carbofuran or trimethacarb enhanced biodegradation of subsequent treatments with the technical formulations. Degradation of carbofuran was enhanced by pretreatments with trimethacarb, and degradation of trimethacarb was enhanced by pretreatments with carbofuran. Bendiocarb degradation was enhanced by pretreatments of soil with carbofuran or trimethacarb. In bioassays with southern corn rootworm larvae, biological activity of carbofuran, trimethacarb, and bendiocarb was rapidly lost in soils pretreated with granular formulations. Pretreatment of soil with granular terbufos did not enhance the biodegradation of subsequent applications of technical terbufos. Several microbial biomass assays showed an increase in specific carbofuran‐degrading bacteria in soils that were pretreated with carbofuran. Bacteria were isolated that could grow on carbofuran and apparently degrade it when present with another carbon source.

Using sentinel plants as biomonitors of herbicide drift and deposition

Abstract Chemical analyses of air and precipitation have documented a widespread occurrence of pesticide residues over both intensively farmed regions and areas remote from agriculture. The health or ecological significance of the low levels detected is obscure, but drift of herbicide residues during spraying has sometimes damaged nearby nontarget crops. Monitoring of herbicide residue deposition, whether resulting from direct drift or following long‐range transport, is highly desirable to determine possible adverse effects on yield. Although chemical assays can confirm the identity of residues, their use in intensive regional sampling studies can be expensive. Certain herbicide groups are difficult to detect. Furthermore, the mere presence of a residue does not easily translate into an assessment of biological effect. Although not as specific as chemical analyses, biological assays with sentinel plants can be used to detect classes of herbicides with unique modes of action and characteristic injury patte...