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Interpreting Water and Soil Monitoring Parameters
A P P E N D I X
F Interpreting Water and Soil Monitoring Parameters
Below are descriptions of various data measurements required for assessing pesticide management. The parameters are grouped into the following categories: • Physicochemical data: microcatchment environmental physicochemical data such as location, topography, temperature, electrical conductivity (EC), dissolved O2, pH, and chemical oxygen demand; • Pesticide monitoring data: both of pesticide usage and residues in water and sediments; and • Biological and toxicity data for “water quality”: which include in situ bioassays and ecological measures such as species richness, biodiversity, and density.
PHYSICOCHEMICAL DATA Initially a series of topographic measurements are required. Many of these measurements would have been made when the microcatchment was selected.
Location Unit of measurement: this must be in the form of some coordinate system, preference being given to a universal system such as latitude and longitude. Description: the coordinates should be in a form that can be read into a geographical information system. For latitude they should be expressed as decimal degrees (to the fifth decimal place or better precision if possible), with southern latitudes being expressed as negative values. Similarly, longitude should be expressed as decimal degrees with western longitudes being expressed as negative numbers. Measurements can be taken with a global positioning system—many modern mobile phones have this as an in-built application. Importance: accurate location is essential for producing maps of the site. It is also important for locating sampling sites.
Slope Unit of measurement: degrees of % slope. Description: the slope of the land may vary within a microcatchment. A value that has an intermediate slope should be measured. Measurements could be taken with a theodolite or an inclinometer. There are some free applications that can be downloaded onto mobile phones with an accuracy that is fit for purpose.
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Importance: slope of the land is important in affecting runoff. This in turn affects the likelihood of direct offsite pesticide movement. It also affects soil erosion.
Vegetation Cover Unit of measurement: typically percent cover. Description: the fraction of an area that is covered by a vertical projection of the vegetation onto the ground. Importance: vegetation cover intercepts most pesticide applications. It also holds water, retards runoff, and reduces soil erosion. There are a series of local weather variables that should be recorded. Ideally these would be measured in an automatic weather station that transmits data back to the base laboratory. The following measurements should be taken—if these are not available some interpolation from other stations would assist but this is not recommended.
Rainfall Unit of measurement: millimeter (mm). Description: the amount of precipitation received, including rain, hail, and snow. This should be recorded with a standard rain gauge so that losses due to evaporation are minimized. Importance: rainfall is a key parameter in assessing, among other things, direct pesticide runoff. It is also a key component in assessing drainage.
Irrigation Unit of measurement: meter (m). Description: this is almost equivalent to rainfall but usually only is applied when the soil is dry. Generally it is assumed that the irrigation is applied uniformly—this may be a dubious assumption and should be kept in mind during the data interpretation phase. Importance: irrigation together with rainfall is a key parameter when assessing runoff and associated direct off-site migration of pesticide residues. It is also a key component in assessing drainage.
Air Temperature Unit of measurement: degrees Celsius. Description: temperature is measured in some type of screen (perhaps a Stephenson screen) or in some automatic recording weather station. Users should be aware of the potential effects of microclimate (such as height of measurement above the ground and local vegetation) that can affect the reading by several degrees. Importance: temperature is a key driver of evapotranspiration. Air temperature is also often used in assessing average soil temperature, which in turn affects pesticide half-life.
Humidity Unit of measurement: percentage humidity. Description: percentage humidity is the ratio of the amount of moisture in the air compared with the amount of moisture required to saturate the air at the same temperature and pressure. Importance: humidity is a key driver of potential evapotranspiration.
Wind Speed and Direction Unit of measurement: meters per second and compass degrees. Description: wind speed is measured using a rotation anemometer. Wind speed varies with height—a common height of measurement is 2 m. Wind speed is usually averaged over an interval (commonly 10 min). Importance: wind speed, combined with temperature and humidity, can be used to predict potential evaporation via the Penman Monteith equations (Allen et al., 1998). Wind speed and direction are important parameters
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for quantifying spray drift but generally this is not known until after spraying so it is of limited value in predicting spray drift.
Potential Evapotranspiration Unit of measurement: millimeters. Description: this is an estimate of water loss given that there is limitation on water supply. This is a difficult measure to maintain so usually it is predicted from temperature, humidity, and wind speed. Importance: evapotranspiration is a key component of water balance, which in turn affects runoff and drainage. Allen et al. (1998) provided a guideline for computing crop water requirements.
Soil Parameters A series of soil parameters are required to understand off-site migration of pesticide residues. A prerequisite of assessing these parameters is to take accurate soils samples. These should be taken with a soil corer and not with a spade. A full understanding of the environment would involve assessment of many soil parameters such as soil nutrient levels. These are not considered in this document as they do not directly affect the off-site migration of pesticides. Two critical parameters are soil texture and soil organic matter. Soil Texture Unit of measurement: this can be expressed as percent coarse sand, fine sand, silt, and clay. A more convenient classification is into texture classes such as sand and sandy loam. Description: the classification into texture classes can be performed by a detailed assessment of the fraction of sand, silt, etc. However, an experienced pedologist can assign a soil to a classification in the field by “feel.” Such a classification will usually be fit for purpose; it also has the advantage of being rapid enabling many sites within the microcatchment to be assessed. Importance: a key significance of soil texture is in the partition of rainfall and irrigation into runoff fraction and to drainage. Total Organic Carbon Unit of measurement: percent on a dry weight basis. Description: generally the organic carbon causes a darkening of the soil—the darkening can be quantified as the “value” in Munsell color charts. However, total organic carbon (TOC) is such an important parameter that it should be quantified in a laboratory from a soil core sample. Importance: many pesticides are at least in part absorbed by soil organic matter. The ability of a soil to retain a pesticide is therefore commonly associated with the TOC.
Water Quality Measures A range of field water quality measures can often be taken with a probe. These include dissolved oxygen (DO), pH, EC, and turbidity. Dissolved Oxygen Units of measurement: concentration in mg/L and percent saturation (%). Saturation values are averaged because a reading taken in the morning may be low due to respiration, while a measurement taken afternoon may show that the saturation has recovered to acceptable levels. Description: a measure of the amount of oxygen in the water. Concentration is a measure of the amount of oxygen in a volume of water; saturation is a measurement of the amount of oxygen in the water compared with the amount of oxygen the water can actually hold at full saturation. Both of these measurements are necessary to accurately determine whether water quality standards are met. Several measurements of oxygen saturation taken in a 24-h period must be averaged to compare with the 75% daily average saturation standard (which is commonly set at 75% saturation).
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Importance: oxygen is dissolved into the water from the atmosphere, aided by wind and wave action, or by rocky, steep, or uneven stream beds and also from photosynthesis. The presence of dissolved oxygen is vital to bottom-dwelling organisms as well as fish and amphibians. Aquatic plants and algae produce oxygen in the water during the day and consume oxygen during the night. Bacteria utilize oxygen both day and night when they process organic matter into smaller and smaller particles. Water pH Unit of measurement: units (no abbreviation). Description: a measure of hydrogen ion activity in water, or, in general terms, the acidity of water. pH is measured on a logarithmic scale of 0 14, with 7 being neutral. A high pH indicates alkaline (or basic) conditions and occurs commonly in areas that are rich in limestone. A low pH indicates acidic conditions which can be caused by organic acids (decaying leaves and other matter) and human activity (including the use of some mineral fertilizers). The normal range for pH is 6 8. Importance: pH affects many chemical and biological processes in the water and this is important to the survival and reproduction of fish and other aquatic life. Different organisms flourish within different ranges of pH. Measurements outside of an organism’s preferred range can limit growth and reproduction and lead to physiological stress. Low pH can also affect the toxicity of aquatic compounds such as ammonia and certain metals by making them more “available” for uptake by aquatic plants and animals. This can produce conditions that are toxic to aquatic life. pH can affect availability of nutrients. It can also affect the dissociation of some pesticides, which in turn affects their rate of degradation and ability to bind with soil. Electrical Conductivity Unit of measurement: micromhos per centimeter (µmhos/cm) or microsiemens per centimeter (µS/cm). Description: EC is a measure of the ability of water to carry an electrical current (typically at 25 C) and is an indirect measure of the free ion (charged particles) content in the water. These ions can come from natural sources such as bedrock or saline groundwater, or human sources such as storm water runoff, waste water, or an accumulation of salt from irrigation. EC is affected by temperature and some compensation should be made if the temperature differs from 25 C. Importance: EC is closely related to salinity and as such is a useful surrogate for ions such as Na1 and Cl2. The relationship between salinity and EC is very good as long as the mixture of ions in the solution remains constant—even when there is some variation in the mixture EC is a very useful guide to salinity. Because of the ease of measurement, high EC specific readings can help locate pollution sources because polluted waters usually have a higher EC than unpolluted waters. Some common pollution sources that have been identified by elevated EC values include pollution from road salt, septic systems, wastewater treatment plants, industrial waste, or urban/agricultural runoff. Turbidity Unit of measurement: nephelometric turbidity units (abbreviated as NTU). Description: a measurement of the amount of scattered and absorption of light in a water sample. The scattering is due to suspended material in the water and depends on the total amount of suspended matter (TSS) and the nature of the material. This material may include particles such as clay, silt, algae, soil organic matter, and decaying plant material, and causes light to be scattered and absorbed. Importance: higher turbidity also reduces the amount of light that can penetrate the water, which reduces photosynthesis and DO production. Suspended materials can clog fish gills, reducing disease resistance, lowering growth rates, and affecting egg and larval development. As the particles settle, they can blanket the stream bottom, especially in slower waters, and smother fish eggs and benthic macroinvertebrates. Clean waters are generally associated with low turbidity, but there is a high degree of natural variability involved. Rain events can increase turbidity in surface waters by flushing sediment, organic matter, and other materials into the water. Human activities such as vegetation removal and soil disruption can also lead to dramatic increases in turbidity levels. Turbidity can also be used as an indicator of TSS although the relationship is not as strong as might be expected. In the absence of other data, turbidity can be used as an indicator of the rate of erosion—this option is used in Pesticide Impact Rating Index (PIRI) to facilitate its use.
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Temperature Unit of measurement: degrees Celsius ( C). Importance: water temperature is a critical parameter for aquatic life and has an impact on other water quality parameters such as DO and bacterial activity. Water temperature controls the metabolic and reproductive processes of aquatic species and can determine which fish and macroinvertebrate species can survive in a given river or stream. Soil temperature is also important in affecting the rate of breakdown of organic matter, and in particular pesticides. Typically, an increase of 10 C will increase the rate of degradation of the pesticide by a factor of 2.58 (European Commission, 2014). Conversely, where there are low temperatures, the half-lives of pesticides increase. A number of factors can have an impact on water temperature including the quantity and maturity of riparian vegetation, the rate of flow, and the percent of impervious surfaces contributing storm water, thermal discharges, impoundments, and groundwater. Flow Unit of measure: liters per second (L/s) or some other measure of volume per time interval. Description: flow is the volume of water passing a given point over a short interval (perhaps 1 s). Measurement is often not possible unless there is a weir where the head of water (which is closely related to flow) can be measured. Ideally the flow will be monitored continuously. Some approximation to flow can be obtained by measuring the speed of water (perhaps using a Doppler technique). An approximation to the speed can be obtained by recording the time some floating object takes to pass between two points which are a known distance apart. However, if a measurement of load is considered important, a purpose-built installation should be installed. Importance: measurement of flow is essential if a load of contaminants is to be assessed. The list of contaminants may be as diverse as total suspended solids or dissolved pesticides. Flow data can be used to assess erosion rates, which in turn may be a reflection of the pesticide load bound to soil. Buffer Strips Unit of measurement: meters. Description: buffer strips can be effective in reducing off-site migration of pesticides by spray drift, erosion, and direct runoff. However, the quality of buffers is often poor, with preferential flow through rills being evident. Generally a conservative approach is recommended and the width of the buffer strip is set to zero. Importance: well-maintained buffer strips can be important as a mitigation measure. Distance and Width of Water Body Unit of measurement: meters. Description: the distance to the nearest water body and its width are used in assessing spray drift. Two key parameters are the distance to the water body (as the amount of spray drift decreases with distance) and the width of the water body. Importance: these parameters are important when spray drift is a significant pathway for off-site migration to a water body. Off-site spray drift is difficult to estimate accurately. Depth to Water Table Unit of measurement: meters. Description: this depth would be the physical distance a contaminant applied at the soil surface would need to travel before it reached groundwater. Typically, the theory for this calculation assumes, at least to some degree, that the soil is uniform. Importance: once a contaminant has passed through the top meter of soil, it has a high chance of continuing to the water table. Accurate measurement of the depth of the water table (provided it is more than 5 m) is therefore not very important.
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PESTICIDE MONITORING DATA Pesticide usage data are vital to understanding the off-site effects of pesticides. The following parameters should be recorded for each pesticide used. Where a formulation contains two pesticides, each active component should be treated separately. These data are collected before or at the time of application of the pesticide.
Rate of Application Unit of measurement: L/ha or kg/ha. Description: the amount of formulation that is applied per hectare. Where it is diluted with water (e.g., 1 L formulation made up to 100 L), the application rate would be calculated as the volume sprayed per hectare multiplied by the dilution factor (in this case 0.01). Importance: an understanding and correct estimation of the rate of application of pesticides is an essential part of quantifying their off-site effects.
Frequency of Application Unit of measurement: count. Description: often a pesticide (especially a fungicide or an insecticide) is applied many times in a season. These applications are potentially additive, especially for a persistent pesticide or if the temperature is low. Importance: there is an enormous variation in pesticide applications even for the same crop. Frequency of application of a single pesticide or a cocktail of pesticides is important information to gather especially for risk assessment purposes. Besides toxicological data, information on the frequency of exposure to a specific pesticide and the time between two applications is used as a starting point for the choice of the most relevant risk assessment model.
Fraction of Active Ingredient Unit of measurement: parts per thousand. Description: typically this is expressed as gram (g) active ingredient per kilogram formulation. The result is therefore a ratio expressed as parts per thousand. It may also be expressed as g/L, which is also expressed as parts per thousand. The “nonactive” part of the formulation may also have off-site effects, but quantifying this would require knowledge of the formulation—this is often not known as it is the intellectual property of the manufacturer. Importance: this parameter performs the appropriate scaling of the area and is an unbiased estimate of the quantity of pesticide used.
Fraction of Area Sprayed Unit of measurement: ratio (no units). Description: in some cases weeds (or other pests) are spot sprayed. This parameter is used to take this into account. The parameter is also useful when there are several crop types within a microcatchment so that the total area can be partitioned. Importance: this parameter performs the appropriate scaling of the area so that an unbiased estimate of the quantity of pesticide used is available.
Droplet Size Unit of measurement: microns. Description: this varies typically with the pesticide being used—herbicides have larger droplet sizes than insecticides. The droplet size is typically determined by the spray nozzle. Ideally the droplet size should have only a small range for a given application type. Importance: droplet size is a key parameter in predicting spray drift. Unlike wind speed it is known at the time of application.
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There are other pesticide parameters that are essential for an understanding of pesticide management. Some of these properties are available in publications but others need to be assessed in the laboratory using soil samples obtained from the field. There are also parameters that should be monitored after spraying. These are listed below.
Spray Drift Deposition Unit of measurement: µg/m2. Description: this measure quantifies off-site spray drift. It requires suitable receptors that are placed at strategic places in nontarget areas. Experience has indicated that Petri dishes are suitable containers. Following spraying the Petri dishes are collected and washed with solvent which is assayed for pesticide. Importance: quantification of off-site drift is important for a range of reasons including potential contamination of water bodies and harm to neighboring crops. Alternatively, if there is some harm to a neighboring crop, absence of spray drift would be evidence that the harm was due to some other cause.
Surface Water Contamination Unit of measurement: µ/L. Description: this is a measure of contamination in a stream. Representative samples should be taken across the flow profile to determine the average concentration of pesticides in water. Importance: the concentration of surface water contaminants is important in assessing the contaminant load. It also assists in the interpretation of biological parameters.
Soil Contamination by Pesticides Unit of measurement: µg/kg. Description: some pesticides bind to and may persist in the soil. The decrease in concentration may be due to pesticide breakdown, uptake by organisms or leaching. The decrease in soil concentration is therefore related to half-life but includes other components. Importance: pesticide residues in soils can have unwanted consequences including harmful effects on soil activity and continuing to be a reservoir for contaminating produce from the field.
Crop/Food Contamination Unit of measurement: µg/kg. Description: some pesticides are detectable in produce from fields. A withholding time may suffice to enable lowering of the contaminant concentration to an acceptable level. In other cases, where a field has been sprayed with a persistent pesticide, residue levels may be excessive many years later. Importance: residue levels in products may have harmful effects on consumers. They may also prevent export of the product to another country. This raises an important laboratory question in that the laboratory responsible for certifying products for export must have equipment at least as sensitive as that of the laboratory monitoring pesticide levels of imports.
Groundwater Contamination Unit of measurement: µg/L. Description: this is a detected amount of pesticide in groundwater. Note that there could be several aquifers and initially the top aquifer should be monitored. Importance: pesticide contamination of groundwater is a subject of high importance because groundwater is often used for drinking water. In earlier times it was thought that soil acted as a filter that stopped pesticides from reaching groundwater. Studies have now shown that this is not the case (USGS, 2006). Pesticides can reach water-bearing aquifers below ground from applications onto crop fields, accidental spills and leaks, improper disposal, and even through injection of waste material into wells. There are many other pesticide properties that can be discussed. Below are a few key parameters.
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Kd Unit of measure: L/kg. Description: Kd is the ability of soil to bind a pesticide. In some cases the pesticide may be charged and may bind to soils in some different manner. Use of Koc and TOC to predict Kd is a useful approximation and is used in such programs as PIRI. While a direct measure of Kd would be preferable it is generally not available for all pesticides in all soils. Importance: Kd is used for predicting the binding of pesticides to soil. This is a key component in predicting off-site movement of pesticides.
Kow Unit of measure: no units—it is a ratio. Description: Kow is a partition constant between n-octanol and water. It is a measure of the concentration of a pesticide in an equal mixture of water and n-octanol. Importance: Kow is a measure of whether the pesticide is likely to accumulate in organic matter (especially lipids) or whether it will stay in the water phase.
Koc Unit of measure: no units—it is a ratio. Description: this is similar to Kow but is the partition between water and soil organic carbon—the higher the Koc the larger the fraction of pesticide that is in the soil organic matter. Typically Koc is derived from Kd and TOC data using the formula: Koc 5
Kd TOC
Once there is an estimate of Koc, an estimate of Kd is then possible using the formula: Kd 5 Koc 3 TOC Importance: Koc is a very important property in that it is a measure of whether a pesticide is likely to move with surface water—pesticides with a high Koc values are less likely to move than those with a low Koc. Koc is an important component in assessing pesticide movement in surface water and its movement to groundwater.
Half-Life Unit of measure: days (in extreme cases it may be measured in hours or years). Description: half-life is the time required for half the pesticide to break down. The rate of breakdown is affected by temperature (Fantke et al., 2014). Half-life is also affected by the amount of biological activity in the soil (typically there is more activity in the surface soil than the subsoil). There are different half-lives for pesticides in water, plant tissue, and soil. There are published data available for the half-lives of pesticides but if possible these should be assessed under local conditions. Importance: a persistent pesticide will remain in an area often longer than is required. Some pesticides such as DDT persist for many years. A persistent pesticide is more likely to reach the water table. Half-life data are therefore vital in choosing an appropriate pesticide for agricultural applications that will cause minimal off-site harm.
BIOLOGICAL AND TOXICITY DATA Biological and toxicity data fall into two categories. The first is centered on laboratory studies, and so can incorporate preexisting data on toxicity. A second approach described below uses field data. We consider first the laboratory approach. The first approach depends on obtaining some estimate of the expected environmental concentration (EEC). That concentration can be compared with a measure of toxicity such as LD50. The ratio of EEC to LD50 is then a toxicity quotient, and this can be used to predict likely harm.
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LD50 Unit of measurement: typically mg/kg. Description: dose of some toxicant that would kill 50% of test animals. Because LD50 varies among species, a selection representing the range of potentially affected organisms should be considered. Importance: LD50 is a measure of the toxicity of the material likely to be ingested. When the LD50 is very low it is unlikely that that chemical will do much harm. However, for some chemicals only a small dose would be harmful.
LC50 Unit of measurement: mg/L is most common, but sometimes given as µg/L. Description: this is the concentration that is lethal to (will kill) 50% of organisms in a given time. Short-term tests (,96 h) measure acute toxicity and longer term tests measure chronic toxicity. The duration of the test time varies with the organism. Generally there is a close relationship between acute and chronic toxicity (see Kumar et al., 2010 for further details). Importance: LC50 gives a measure of the toxicity of a compound (or mixture). Although a lower dose as indicated by an LC50 (which would kill 5% of the organisms) would be better, this is difficult to measure and there are less data available. LC50 is therefore a key parameter in assessing toxicity, but allowance should be made so that only a small fraction of the organisms are affected (often a factor of 10 is used), and perhaps allowance for chronic toxicity as well as acute toxicity.
EC50 Unit of measurement: mg/L is most common but sometimes given as µg/L. Description: EC50 is a concentration that reduces some measure of biological activity to 50% of the base rate. It is a generic term and is applied to measures that include features as diverse as respiration, specific enzyme activity, and rates of growth of algae. As with LC50, a more desirable measure from an ecological approach would be EC50 but this is difficult to measure accurately. Importance: EC50 can be applied to a wide range of environmental parameters and can give an indication (e.g., through reduced enzyme activity) before there is any effect that is obvious. Field-based measurements of toxicity reflect what is actually occurring in the field. Several techniques are described below.
Passive Samplers Unit of measurement: qualitative and semiquantitative measure. Description: passive samplers are intended to mimic the absorption of contaminants (especially lipophilic contaminants) by placing some material in the water. The sampler is later recovered and analyzed for contaminants. The rate of uptake of a contaminant varies with water speed and contaminant concentration. Results from passive samplers are therefore at best semiquantitative. Importance: passive samplers are receptive over the interval of immersion. They are therefore likely to detect a pulse of contaminant that would have been missed by more conventional grab sampling.
In Situ Toxicity Testing Unit of measurement: percentage mortality. Description: typically this is performed using caged animals. Several caged animals are placed in a stream for a period depending on the nature of the test animal. At the end of the interval the cage is recovered and the number of deaths noted. Typically several cages should be deployed so that an effect is applicable to more than that one cage. It is also necessary to deploy cages in noncontaminated streams to ensure that deaths would not have occurred just through the experimental technique.
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Importance: in situ tests represent the actual conditions, and reflect more closely the exposure conditions. The in situ technique bypasses issues such as the effect of mixtures and water speed and of interactions between contaminants and other local environmental measures such as interactions with pH or water hardness.
Changes in Biodiversity Unit of measurement: depends on measure of biodiversity. Description: the impact of pesticides (or change in pesticide management) may affect the biodiversity of a river. This can be assessed by biomonitoring, by comparing the biodiversity in the impacted site with that in control or reference sites. Importance: a well-constructed design can give an indication of the combined off-site effects of pesticides and other pollutants.
References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration Guidelines for Computing Crop Water Requirements. FAO Irrigation and Drainage Paper 56, FAO, Rome92-5-104219-5. European Commission, 2014. Assessing Potential for Movement of Active Substances and their Metabolites to Ground Water in the EU. Report of the FOCUS Ground Water Work Group, EC Document Reference Sanco/13144/2010 version 3, 613 pp. Fantke, P., Gillespie, B.W., Juraske, R., Jolliet, O., 2014. Estimating half-lives for pesticide dissipation from plants. Environ. Sci. Technol. 48, 8588 8602. Kumar, A., Correll, R., Grocke, S., Bajet, C., 2010. Toxicity of selected pesticides to freshwater shrimp, Paratya australiensis (Decapoda: Atyidae): use of time series acute toxicity data to predict chronic lethality. Ecotoxicol. Environ. Saf. 73, 360 369. USGS, 2006. Pesticides in the Nation’s Streams and Ground Water, 1992 2001 a summary. Available from: ,http://pubs.usgs.gov/fs/ 2006/3028/pdf/fs2006-3028.pdf..
F Interpreting Water and Soil Monitoring Parameters
Below are descriptions of various data measurements required for assessing pesticide management. The parameters are grouped into the following categories: • Physicochemical data: microcatchment environmental physicochemical data such as location, topography, temperature, electrical conductivity (EC), dissolved O2, pH, and chemical oxygen demand; • Pesticide monitoring data: both of pesticide usage and residues in water and sediments; and • Biological and toxicity data for “water quality”: which include in situ bioassays and ecological measures such as species richness, biodiversity, and density.
PHYSICOCHEMICAL DATA Initially a series of topographic measurements are required. Many of these measurements would have been made when the microcatchment was selected.
Location Unit of measurement: this must be in the form of some coordinate system, preference being given to a universal system such as latitude and longitude. Description: the coordinates should be in a form that can be read into a geographical information system. For latitude they should be expressed as decimal degrees (to the fifth decimal place or better precision if possible), with southern latitudes being expressed as negative values. Similarly, longitude should be expressed as decimal degrees with western longitudes being expressed as negative numbers. Measurements can be taken with a global positioning system—many modern mobile phones have this as an in-built application. Importance: accurate location is essential for producing maps of the site. It is also important for locating sampling sites.
Slope Unit of measurement: degrees of % slope. Description: the slope of the land may vary within a microcatchment. A value that has an intermediate slope should be measured. Measurements could be taken with a theodolite or an inclinometer. There are some free applications that can be downloaded onto mobile phones with an accuracy that is fit for purpose.
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Importance: slope of the land is important in affecting runoff. This in turn affects the likelihood of direct offsite pesticide movement. It also affects soil erosion.
Vegetation Cover Unit of measurement: typically percent cover. Description: the fraction of an area that is covered by a vertical projection of the vegetation onto the ground. Importance: vegetation cover intercepts most pesticide applications. It also holds water, retards runoff, and reduces soil erosion. There are a series of local weather variables that should be recorded. Ideally these would be measured in an automatic weather station that transmits data back to the base laboratory. The following measurements should be taken—if these are not available some interpolation from other stations would assist but this is not recommended.
Rainfall Unit of measurement: millimeter (mm). Description: the amount of precipitation received, including rain, hail, and snow. This should be recorded with a standard rain gauge so that losses due to evaporation are minimized. Importance: rainfall is a key parameter in assessing, among other things, direct pesticide runoff. It is also a key component in assessing drainage.
Irrigation Unit of measurement: meter (m). Description: this is almost equivalent to rainfall but usually only is applied when the soil is dry. Generally it is assumed that the irrigation is applied uniformly—this may be a dubious assumption and should be kept in mind during the data interpretation phase. Importance: irrigation together with rainfall is a key parameter when assessing runoff and associated direct off-site migration of pesticide residues. It is also a key component in assessing drainage.
Air Temperature Unit of measurement: degrees Celsius. Description: temperature is measured in some type of screen (perhaps a Stephenson screen) or in some automatic recording weather station. Users should be aware of the potential effects of microclimate (such as height of measurement above the ground and local vegetation) that can affect the reading by several degrees. Importance: temperature is a key driver of evapotranspiration. Air temperature is also often used in assessing average soil temperature, which in turn affects pesticide half-life.
Humidity Unit of measurement: percentage humidity. Description: percentage humidity is the ratio of the amount of moisture in the air compared with the amount of moisture required to saturate the air at the same temperature and pressure. Importance: humidity is a key driver of potential evapotranspiration.
Wind Speed and Direction Unit of measurement: meters per second and compass degrees. Description: wind speed is measured using a rotation anemometer. Wind speed varies with height—a common height of measurement is 2 m. Wind speed is usually averaged over an interval (commonly 10 min). Importance: wind speed, combined with temperature and humidity, can be used to predict potential evaporation via the Penman Monteith equations (Allen et al., 1998). Wind speed and direction are important parameters
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for quantifying spray drift but generally this is not known until after spraying so it is of limited value in predicting spray drift.
Potential Evapotranspiration Unit of measurement: millimeters. Description: this is an estimate of water loss given that there is limitation on water supply. This is a difficult measure to maintain so usually it is predicted from temperature, humidity, and wind speed. Importance: evapotranspiration is a key component of water balance, which in turn affects runoff and drainage. Allen et al. (1998) provided a guideline for computing crop water requirements.
Soil Parameters A series of soil parameters are required to understand off-site migration of pesticide residues. A prerequisite of assessing these parameters is to take accurate soils samples. These should be taken with a soil corer and not with a spade. A full understanding of the environment would involve assessment of many soil parameters such as soil nutrient levels. These are not considered in this document as they do not directly affect the off-site migration of pesticides. Two critical parameters are soil texture and soil organic matter. Soil Texture Unit of measurement: this can be expressed as percent coarse sand, fine sand, silt, and clay. A more convenient classification is into texture classes such as sand and sandy loam. Description: the classification into texture classes can be performed by a detailed assessment of the fraction of sand, silt, etc. However, an experienced pedologist can assign a soil to a classification in the field by “feel.” Such a classification will usually be fit for purpose; it also has the advantage of being rapid enabling many sites within the microcatchment to be assessed. Importance: a key significance of soil texture is in the partition of rainfall and irrigation into runoff fraction and to drainage. Total Organic Carbon Unit of measurement: percent on a dry weight basis. Description: generally the organic carbon causes a darkening of the soil—the darkening can be quantified as the “value” in Munsell color charts. However, total organic carbon (TOC) is such an important parameter that it should be quantified in a laboratory from a soil core sample. Importance: many pesticides are at least in part absorbed by soil organic matter. The ability of a soil to retain a pesticide is therefore commonly associated with the TOC.
Water Quality Measures A range of field water quality measures can often be taken with a probe. These include dissolved oxygen (DO), pH, EC, and turbidity. Dissolved Oxygen Units of measurement: concentration in mg/L and percent saturation (%). Saturation values are averaged because a reading taken in the morning may be low due to respiration, while a measurement taken afternoon may show that the saturation has recovered to acceptable levels. Description: a measure of the amount of oxygen in the water. Concentration is a measure of the amount of oxygen in a volume of water; saturation is a measurement of the amount of oxygen in the water compared with the amount of oxygen the water can actually hold at full saturation. Both of these measurements are necessary to accurately determine whether water quality standards are met. Several measurements of oxygen saturation taken in a 24-h period must be averaged to compare with the 75% daily average saturation standard (which is commonly set at 75% saturation).
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Importance: oxygen is dissolved into the water from the atmosphere, aided by wind and wave action, or by rocky, steep, or uneven stream beds and also from photosynthesis. The presence of dissolved oxygen is vital to bottom-dwelling organisms as well as fish and amphibians. Aquatic plants and algae produce oxygen in the water during the day and consume oxygen during the night. Bacteria utilize oxygen both day and night when they process organic matter into smaller and smaller particles. Water pH Unit of measurement: units (no abbreviation). Description: a measure of hydrogen ion activity in water, or, in general terms, the acidity of water. pH is measured on a logarithmic scale of 0 14, with 7 being neutral. A high pH indicates alkaline (or basic) conditions and occurs commonly in areas that are rich in limestone. A low pH indicates acidic conditions which can be caused by organic acids (decaying leaves and other matter) and human activity (including the use of some mineral fertilizers). The normal range for pH is 6 8. Importance: pH affects many chemical and biological processes in the water and this is important to the survival and reproduction of fish and other aquatic life. Different organisms flourish within different ranges of pH. Measurements outside of an organism’s preferred range can limit growth and reproduction and lead to physiological stress. Low pH can also affect the toxicity of aquatic compounds such as ammonia and certain metals by making them more “available” for uptake by aquatic plants and animals. This can produce conditions that are toxic to aquatic life. pH can affect availability of nutrients. It can also affect the dissociation of some pesticides, which in turn affects their rate of degradation and ability to bind with soil. Electrical Conductivity Unit of measurement: micromhos per centimeter (µmhos/cm) or microsiemens per centimeter (µS/cm). Description: EC is a measure of the ability of water to carry an electrical current (typically at 25 C) and is an indirect measure of the free ion (charged particles) content in the water. These ions can come from natural sources such as bedrock or saline groundwater, or human sources such as storm water runoff, waste water, or an accumulation of salt from irrigation. EC is affected by temperature and some compensation should be made if the temperature differs from 25 C. Importance: EC is closely related to salinity and as such is a useful surrogate for ions such as Na1 and Cl2. The relationship between salinity and EC is very good as long as the mixture of ions in the solution remains constant—even when there is some variation in the mixture EC is a very useful guide to salinity. Because of the ease of measurement, high EC specific readings can help locate pollution sources because polluted waters usually have a higher EC than unpolluted waters. Some common pollution sources that have been identified by elevated EC values include pollution from road salt, septic systems, wastewater treatment plants, industrial waste, or urban/agricultural runoff. Turbidity Unit of measurement: nephelometric turbidity units (abbreviated as NTU). Description: a measurement of the amount of scattered and absorption of light in a water sample. The scattering is due to suspended material in the water and depends on the total amount of suspended matter (TSS) and the nature of the material. This material may include particles such as clay, silt, algae, soil organic matter, and decaying plant material, and causes light to be scattered and absorbed. Importance: higher turbidity also reduces the amount of light that can penetrate the water, which reduces photosynthesis and DO production. Suspended materials can clog fish gills, reducing disease resistance, lowering growth rates, and affecting egg and larval development. As the particles settle, they can blanket the stream bottom, especially in slower waters, and smother fish eggs and benthic macroinvertebrates. Clean waters are generally associated with low turbidity, but there is a high degree of natural variability involved. Rain events can increase turbidity in surface waters by flushing sediment, organic matter, and other materials into the water. Human activities such as vegetation removal and soil disruption can also lead to dramatic increases in turbidity levels. Turbidity can also be used as an indicator of TSS although the relationship is not as strong as might be expected. In the absence of other data, turbidity can be used as an indicator of the rate of erosion—this option is used in Pesticide Impact Rating Index (PIRI) to facilitate its use.
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Temperature Unit of measurement: degrees Celsius ( C). Importance: water temperature is a critical parameter for aquatic life and has an impact on other water quality parameters such as DO and bacterial activity. Water temperature controls the metabolic and reproductive processes of aquatic species and can determine which fish and macroinvertebrate species can survive in a given river or stream. Soil temperature is also important in affecting the rate of breakdown of organic matter, and in particular pesticides. Typically, an increase of 10 C will increase the rate of degradation of the pesticide by a factor of 2.58 (European Commission, 2014). Conversely, where there are low temperatures, the half-lives of pesticides increase. A number of factors can have an impact on water temperature including the quantity and maturity of riparian vegetation, the rate of flow, and the percent of impervious surfaces contributing storm water, thermal discharges, impoundments, and groundwater. Flow Unit of measure: liters per second (L/s) or some other measure of volume per time interval. Description: flow is the volume of water passing a given point over a short interval (perhaps 1 s). Measurement is often not possible unless there is a weir where the head of water (which is closely related to flow) can be measured. Ideally the flow will be monitored continuously. Some approximation to flow can be obtained by measuring the speed of water (perhaps using a Doppler technique). An approximation to the speed can be obtained by recording the time some floating object takes to pass between two points which are a known distance apart. However, if a measurement of load is considered important, a purpose-built installation should be installed. Importance: measurement of flow is essential if a load of contaminants is to be assessed. The list of contaminants may be as diverse as total suspended solids or dissolved pesticides. Flow data can be used to assess erosion rates, which in turn may be a reflection of the pesticide load bound to soil. Buffer Strips Unit of measurement: meters. Description: buffer strips can be effective in reducing off-site migration of pesticides by spray drift, erosion, and direct runoff. However, the quality of buffers is often poor, with preferential flow through rills being evident. Generally a conservative approach is recommended and the width of the buffer strip is set to zero. Importance: well-maintained buffer strips can be important as a mitigation measure. Distance and Width of Water Body Unit of measurement: meters. Description: the distance to the nearest water body and its width are used in assessing spray drift. Two key parameters are the distance to the water body (as the amount of spray drift decreases with distance) and the width of the water body. Importance: these parameters are important when spray drift is a significant pathway for off-site migration to a water body. Off-site spray drift is difficult to estimate accurately. Depth to Water Table Unit of measurement: meters. Description: this depth would be the physical distance a contaminant applied at the soil surface would need to travel before it reached groundwater. Typically, the theory for this calculation assumes, at least to some degree, that the soil is uniform. Importance: once a contaminant has passed through the top meter of soil, it has a high chance of continuing to the water table. Accurate measurement of the depth of the water table (provided it is more than 5 m) is therefore not very important.
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PESTICIDE MONITORING DATA Pesticide usage data are vital to understanding the off-site effects of pesticides. The following parameters should be recorded for each pesticide used. Where a formulation contains two pesticides, each active component should be treated separately. These data are collected before or at the time of application of the pesticide.
Rate of Application Unit of measurement: L/ha or kg/ha. Description: the amount of formulation that is applied per hectare. Where it is diluted with water (e.g., 1 L formulation made up to 100 L), the application rate would be calculated as the volume sprayed per hectare multiplied by the dilution factor (in this case 0.01). Importance: an understanding and correct estimation of the rate of application of pesticides is an essential part of quantifying their off-site effects.
Frequency of Application Unit of measurement: count. Description: often a pesticide (especially a fungicide or an insecticide) is applied many times in a season. These applications are potentially additive, especially for a persistent pesticide or if the temperature is low. Importance: there is an enormous variation in pesticide applications even for the same crop. Frequency of application of a single pesticide or a cocktail of pesticides is important information to gather especially for risk assessment purposes. Besides toxicological data, information on the frequency of exposure to a specific pesticide and the time between two applications is used as a starting point for the choice of the most relevant risk assessment model.
Fraction of Active Ingredient Unit of measurement: parts per thousand. Description: typically this is expressed as gram (g) active ingredient per kilogram formulation. The result is therefore a ratio expressed as parts per thousand. It may also be expressed as g/L, which is also expressed as parts per thousand. The “nonactive” part of the formulation may also have off-site effects, but quantifying this would require knowledge of the formulation—this is often not known as it is the intellectual property of the manufacturer. Importance: this parameter performs the appropriate scaling of the area and is an unbiased estimate of the quantity of pesticide used.
Fraction of Area Sprayed Unit of measurement: ratio (no units). Description: in some cases weeds (or other pests) are spot sprayed. This parameter is used to take this into account. The parameter is also useful when there are several crop types within a microcatchment so that the total area can be partitioned. Importance: this parameter performs the appropriate scaling of the area so that an unbiased estimate of the quantity of pesticide used is available.
Droplet Size Unit of measurement: microns. Description: this varies typically with the pesticide being used—herbicides have larger droplet sizes than insecticides. The droplet size is typically determined by the spray nozzle. Ideally the droplet size should have only a small range for a given application type. Importance: droplet size is a key parameter in predicting spray drift. Unlike wind speed it is known at the time of application.
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There are other pesticide parameters that are essential for an understanding of pesticide management. Some of these properties are available in publications but others need to be assessed in the laboratory using soil samples obtained from the field. There are also parameters that should be monitored after spraying. These are listed below.
Spray Drift Deposition Unit of measurement: µg/m2. Description: this measure quantifies off-site spray drift. It requires suitable receptors that are placed at strategic places in nontarget areas. Experience has indicated that Petri dishes are suitable containers. Following spraying the Petri dishes are collected and washed with solvent which is assayed for pesticide. Importance: quantification of off-site drift is important for a range of reasons including potential contamination of water bodies and harm to neighboring crops. Alternatively, if there is some harm to a neighboring crop, absence of spray drift would be evidence that the harm was due to some other cause.
Surface Water Contamination Unit of measurement: µ/L. Description: this is a measure of contamination in a stream. Representative samples should be taken across the flow profile to determine the average concentration of pesticides in water. Importance: the concentration of surface water contaminants is important in assessing the contaminant load. It also assists in the interpretation of biological parameters.
Soil Contamination by Pesticides Unit of measurement: µg/kg. Description: some pesticides bind to and may persist in the soil. The decrease in concentration may be due to pesticide breakdown, uptake by organisms or leaching. The decrease in soil concentration is therefore related to half-life but includes other components. Importance: pesticide residues in soils can have unwanted consequences including harmful effects on soil activity and continuing to be a reservoir for contaminating produce from the field.
Crop/Food Contamination Unit of measurement: µg/kg. Description: some pesticides are detectable in produce from fields. A withholding time may suffice to enable lowering of the contaminant concentration to an acceptable level. In other cases, where a field has been sprayed with a persistent pesticide, residue levels may be excessive many years later. Importance: residue levels in products may have harmful effects on consumers. They may also prevent export of the product to another country. This raises an important laboratory question in that the laboratory responsible for certifying products for export must have equipment at least as sensitive as that of the laboratory monitoring pesticide levels of imports.
Groundwater Contamination Unit of measurement: µg/L. Description: this is a detected amount of pesticide in groundwater. Note that there could be several aquifers and initially the top aquifer should be monitored. Importance: pesticide contamination of groundwater is a subject of high importance because groundwater is often used for drinking water. In earlier times it was thought that soil acted as a filter that stopped pesticides from reaching groundwater. Studies have now shown that this is not the case (USGS, 2006). Pesticides can reach water-bearing aquifers below ground from applications onto crop fields, accidental spills and leaks, improper disposal, and even through injection of waste material into wells. There are many other pesticide properties that can be discussed. Below are a few key parameters.
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Kd Unit of measure: L/kg. Description: Kd is the ability of soil to bind a pesticide. In some cases the pesticide may be charged and may bind to soils in some different manner. Use of Koc and TOC to predict Kd is a useful approximation and is used in such programs as PIRI. While a direct measure of Kd would be preferable it is generally not available for all pesticides in all soils. Importance: Kd is used for predicting the binding of pesticides to soil. This is a key component in predicting off-site movement of pesticides.
Kow Unit of measure: no units—it is a ratio. Description: Kow is a partition constant between n-octanol and water. It is a measure of the concentration of a pesticide in an equal mixture of water and n-octanol. Importance: Kow is a measure of whether the pesticide is likely to accumulate in organic matter (especially lipids) or whether it will stay in the water phase.
Koc Unit of measure: no units—it is a ratio. Description: this is similar to Kow but is the partition between water and soil organic carbon—the higher the Koc the larger the fraction of pesticide that is in the soil organic matter. Typically Koc is derived from Kd and TOC data using the formula: Koc 5
Kd TOC
Once there is an estimate of Koc, an estimate of Kd is then possible using the formula: Kd 5 Koc 3 TOC Importance: Koc is a very important property in that it is a measure of whether a pesticide is likely to move with surface water—pesticides with a high Koc values are less likely to move than those with a low Koc. Koc is an important component in assessing pesticide movement in surface water and its movement to groundwater.
Half-Life Unit of measure: days (in extreme cases it may be measured in hours or years). Description: half-life is the time required for half the pesticide to break down. The rate of breakdown is affected by temperature (Fantke et al., 2014). Half-life is also affected by the amount of biological activity in the soil (typically there is more activity in the surface soil than the subsoil). There are different half-lives for pesticides in water, plant tissue, and soil. There are published data available for the half-lives of pesticides but if possible these should be assessed under local conditions. Importance: a persistent pesticide will remain in an area often longer than is required. Some pesticides such as DDT persist for many years. A persistent pesticide is more likely to reach the water table. Half-life data are therefore vital in choosing an appropriate pesticide for agricultural applications that will cause minimal off-site harm.
BIOLOGICAL AND TOXICITY DATA Biological and toxicity data fall into two categories. The first is centered on laboratory studies, and so can incorporate preexisting data on toxicity. A second approach described below uses field data. We consider first the laboratory approach. The first approach depends on obtaining some estimate of the expected environmental concentration (EEC). That concentration can be compared with a measure of toxicity such as LD50. The ratio of EEC to LD50 is then a toxicity quotient, and this can be used to predict likely harm.
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LD50 Unit of measurement: typically mg/kg. Description: dose of some toxicant that would kill 50% of test animals. Because LD50 varies among species, a selection representing the range of potentially affected organisms should be considered. Importance: LD50 is a measure of the toxicity of the material likely to be ingested. When the LD50 is very low it is unlikely that that chemical will do much harm. However, for some chemicals only a small dose would be harmful.
LC50 Unit of measurement: mg/L is most common, but sometimes given as µg/L. Description: this is the concentration that is lethal to (will kill) 50% of organisms in a given time. Short-term tests (,96 h) measure acute toxicity and longer term tests measure chronic toxicity. The duration of the test time varies with the organism. Generally there is a close relationship between acute and chronic toxicity (see Kumar et al., 2010 for further details). Importance: LC50 gives a measure of the toxicity of a compound (or mixture). Although a lower dose as indicated by an LC50 (which would kill 5% of the organisms) would be better, this is difficult to measure and there are less data available. LC50 is therefore a key parameter in assessing toxicity, but allowance should be made so that only a small fraction of the organisms are affected (often a factor of 10 is used), and perhaps allowance for chronic toxicity as well as acute toxicity.
EC50 Unit of measurement: mg/L is most common but sometimes given as µg/L. Description: EC50 is a concentration that reduces some measure of biological activity to 50% of the base rate. It is a generic term and is applied to measures that include features as diverse as respiration, specific enzyme activity, and rates of growth of algae. As with LC50, a more desirable measure from an ecological approach would be EC50 but this is difficult to measure accurately. Importance: EC50 can be applied to a wide range of environmental parameters and can give an indication (e.g., through reduced enzyme activity) before there is any effect that is obvious. Field-based measurements of toxicity reflect what is actually occurring in the field. Several techniques are described below.
Passive Samplers Unit of measurement: qualitative and semiquantitative measure. Description: passive samplers are intended to mimic the absorption of contaminants (especially lipophilic contaminants) by placing some material in the water. The sampler is later recovered and analyzed for contaminants. The rate of uptake of a contaminant varies with water speed and contaminant concentration. Results from passive samplers are therefore at best semiquantitative. Importance: passive samplers are receptive over the interval of immersion. They are therefore likely to detect a pulse of contaminant that would have been missed by more conventional grab sampling.
In Situ Toxicity Testing Unit of measurement: percentage mortality. Description: typically this is performed using caged animals. Several caged animals are placed in a stream for a period depending on the nature of the test animal. At the end of the interval the cage is recovered and the number of deaths noted. Typically several cages should be deployed so that an effect is applicable to more than that one cage. It is also necessary to deploy cages in noncontaminated streams to ensure that deaths would not have occurred just through the experimental technique.
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Importance: in situ tests represent the actual conditions, and reflect more closely the exposure conditions. The in situ technique bypasses issues such as the effect of mixtures and water speed and of interactions between contaminants and other local environmental measures such as interactions with pH or water hardness.
Changes in Biodiversity Unit of measurement: depends on measure of biodiversity. Description: the impact of pesticides (or change in pesticide management) may affect the biodiversity of a river. This can be assessed by biomonitoring, by comparing the biodiversity in the impacted site with that in control or reference sites. Importance: a well-constructed design can give an indication of the combined off-site effects of pesticides and other pollutants.
References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration Guidelines for Computing Crop Water Requirements. FAO Irrigation and Drainage Paper 56, FAO, Rome92-5-104219-5. European Commission, 2014. Assessing Potential for Movement of Active Substances and their Metabolites to Ground Water in the EU. Report of the FOCUS Ground Water Work Group, EC Document Reference Sanco/13144/2010 version 3, 613 pp. Fantke, P., Gillespie, B.W., Juraske, R., Jolliet, O., 2014. Estimating half-lives for pesticide dissipation from plants. Environ. Sci. Technol. 48, 8588 8602. Kumar, A., Correll, R., Grocke, S., Bajet, C., 2010. Toxicity of selected pesticides to freshwater shrimp, Paratya australiensis (Decapoda: Atyidae): use of time series acute toxicity data to predict chronic lethality. Ecotoxicol. Environ. Saf. 73, 360 369. USGS, 2006. Pesticides in the Nation’s Streams and Ground Water, 1992 2001 a summary. Available from: ,http://pubs.usgs.gov/fs/ 2006/3028/pdf/fs2006-3028.pdf..