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Agricultural Water Management 106 (2012) 78– 85

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Agricultural Water Management

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Off-site transport of pesticides in dissolved and particulate forms from two landuses in the Mt. Lofty Ranges, South Australia

Danielle P. Olivera,∗, Rai. S. Kookanaa, Jenny S. Andersona, James W. Coxb, Natasha Wallerc,Lester H. Smitha

a CSIRO Land and Water, Water for a Healthy Country, National Research Flagship, PMB 2, Glen Osmond, South Australia 5064, Australiab University of Adelaide, PMB 1, Glen Osmond, South Australia 5064, Australiac Australian Antarctic Division, 203 Channel Highway, Kingston Tasmania 7050, Australia

a r t i c l e i n f o

Article history:Received 20 July 2011Accepted 1 November 2011Available online 21 November 2011

Keywords:PesticideSurface waterOff-site transportTransport mode

a b s t r a c t

The form in which pesticides are transported off-site can have implications for their bioavailability, eco-toxicological impact and the effectiveness of any management strategies implemented to minimise theirmovement. We have investigated the form in which nine pesticides (carbaryl, fenarimol, azinphos methyl,penconazole, pirimicarb, chlorpyrifos, propiconazole, procymidone and bupirimate) were transported insurface water from an apple and cherry orchard in the Mt. Lofty Ranges, South Australia, over three years.The majority of pesticides monitored were found to move off-site in the dissolved (<1.2 �m) phase. Onlypropiconazole moved off-site predominantly (70–90%) by colloidal transport in association with partic-ulate (>1.2 �m) material. Chlorpyrifos was detected in surface drainage water for several months andthe predominant phase in which it moved varied between events in a year and during an event. Theeffectiveness of pesticide physicochemical properties as surrogates for predicting mode of transport ofpesticides, in this region was determined by regression of average proportion (%) of each pesticide in thedissolved phase for each event against the relevant physicochemical parameters. There was no relation-ship between average proportion in the dissolved phase (<1.2 �m) and any of the pesticide characteristicsconsidered. This suggests that off-site transport of pesticides is governed by complex biological andhydrological interactions and the use of simple physicochemical properties as surrogates for predictingoffsite transport may not be applicable. These results have implications for the effectiveness of man-agement strategies, including buffer strips and sedimentation ponds, to minimise transport and suggestthat, unless adequate residency time is available for sorption of the pesticides, these strategies may havelimited use for minimising the transport of the pesticides used in the two land uses studied here. Thisstudy has highlighted the importance of understanding the mode of transport of pesticides for informingthe choice of management strategies to minimise potential offsite transport of pesticides under differentfield conditions.

Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

1. Introduction

Modern agricultural practices, while resulting in increasedyields, may also result in off-site transport of contaminants, includ-ing nutrients, sediment and pesticides, which is of concern tolandholders, regulatory agencies and the general public. The pres-ence of contaminants in waterways can cause eutrophication andecotoxicological effects on aquatic organisms, which may increasethe cost of water treatment for a potable water source. Pesticidescan move off-site through various pathways, namely in the dis-solved phase in runoff water, with soil particles during erosion andwith spray drift of droplets. The form in which pesticides move

∗ Corresponding author. Tel.: +61 8 83038434; fax: +61 8 83038565.E-mail address: Danni.Oliver@csiro.au (D.P. Oliver).

off-site in drainage water (i.e. dissolved or associated with colloids)can have implications for their bioavailability and ecotoxicolgicalimpact as well as the effectiveness of any management strategiesimplemented to minimise their movement. For example, the use ofbuffer strips is often recommended to minimise off-site transportof pesticides (Reichenberger et al., 2007) but this strategy will havelimited effectiveness for those chemicals that move primarily ina dissolved phase unless there is adequate time for the pesticidesto sorb to soil. There are several programmes in North Americathat have monitored pesticides for long periods of time but inthe case of the USGS National Water Quality Assessment program(Gilliom et al., 2007), one of the largest monitoring programmes,the samples were filtered prior to analysis. Studies in ChesapeakeBay tributaries have also filtered samples prior to pesticide analy-ses (Harman-Fetcho et al., 1999; Lehotay et al., 1998). While thisis a common practice, it may underestimate the concentrations of

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compounds that have strong affinities for suspended particles. Anumber of pesticides are preferentially transported adsorbed tosediments (Leonard, 1988). Wauchope (1978) found only thosepesticides with solubilities below 1 mg L−1 to be transported pri-marily by sediment. This is an important mechanism of off-sitetransport of pesticides that should not be overlooked. A numberof suggested management strategies in the literature, such as theuse of flocculant products (e.g. PAM), buffer strips and sedimenta-tion ponds, are aimed primarily at chemicals moving in associationwith colloidals (Reichenberger et al., 2007; Schulz, 2004). Many ofthese strategies depend on pesticides being attached to sediment tosettle out of solution and/or on adequate residence time for pesti-cides in solution to either sorb to soil or sediment or degrade. Thesestrategies may have limited effectiveness if pesticides are movingpredominantly in a dissolved phase or if there is insufficient res-idence time for pesticides to sorb or degrade, as would occur insloping regions or during periods of rapid water flow.

The main objective of this study was to quantify the distributionof pesticides, transported off-site in surface water, between the dis-solved and particulate-associated fractions. An understanding ofthe form in which pesticides are moving off-site can be used toguide management and management strategies to minimise theiroff-site impact. The relationship between the loads of pesticidestransported off-site in relation to individual hydrological eventsand events throughout the year is given elsewhere (Oliver et al.,2012a). In our study water samples were collected from two mainland uses (apples and cherries) over approximately three years andanalysed for pesticide residues. Both unfiltered (total) and filtered(dissolved) samples were analysed and the portion being trans-ported in association with colloids was determined by difference.

2. Materials and methods

2.1. Site selection, instrumentation and water sampling

The field study area in the Mt. Lofty Ranges (MLR) catchmenthas a typical Mediterranean climate (total average annual rainfall1015 mm) with cool (6.0–12.5 ◦C), wet winters (June to August) anddry, hot (11.5–26.1 ◦C) summers (December to February). Gener-ally, there are less frequent rain events from December to April andthere are longer dry periods between rain events during this period.Occasionally however, there is sufficient rainfall to result in a runoffevent in late December to April but for a runoff event to occur duringthis period approximately > 10 mm rainfall is required. The major-ity of rainfall occurs between April/May and August/September (i.e.autumn to winter) and it is more frequent and of greater quantitiesduring this period. A more detailed analysis of transport of loads ofpesticides from the sites in relation to hydrological events is givenin Oliver et al. (2012a).

An apple orchard and a cherry orchard were selected for moni-toring because they were hydrologically isolated and had no othersources of pesticides upstream of these sites. The apple orchardcatchment was 64 ha but the area planted to apples was 34.6 ha.The apple orchard was originally planted to apples in the 1950sbut the current varieties ranged in age from 7 to 51 years old withthe majority over 15 years old. The 8 ha cherry orchard was plantedto 4 ha of cherries that ranged in age from 1 to 10 years old. In boththe cherry and apple orchard the average row width was 4 m. Themain pathway of pesticide transport at both sites is surface and sub-surface flow. There would be negligible contribution to pesticidetransport by spray drift since there is such a long time period (>50days) between the last pesticide application and the first runoffevent. This is discussed further in Oliver et al. (2012b).

Although there are seasonal variations, in general, herbicidesare applied only once or twice during the season around May to

June, and again in November to December in both apple and cherryproduction. Insecticides and fungicides are sprayed usually fromearly to mid September to late February in apple production, andfrom mid to late August to December in cherry production. Duringthe main production period (November to February) apples andcherries are irrigated by overhead and/or drip irrigation, since thereis insufficient rainfall for tree growth, but this was not observed toresult in any runoff for all three years of the study.

At both sites the main soil type was a Red Yellow Chromosol(Isbell, 2002), which dominates 60% of the MLR region. At the appleorchard the organic carbon (OC) content ranged from 1.5% to 6.9%,pH (1:1 water) ranged from 5.4 to 7.5 and clay content (<0.002 mm)ranged from 16% to 35%. At the cherry orchard the OC contentranged from 2.5% to 6.3%, pH (1:1 water) ranged from 5.2 to 6.9, andclay content (<0.002 mm) ranged from 19% to 30%. Both sites weremoderately steep, which is fairly common for horticultural produc-tion in the MLR. The maximum slope was 30◦ and the mean slopewas 13◦. The alleys between tree lines in both the apple and cherryorchards were sown with various grass species such as Festuca sp.(dwarf fescue), Pennisetum purpurium (napier) and Hordeum hystrix(barley grass). As needed the grass was mown and the clippingswere spread along the trees lines as mulch. The distance of thegrassed area between the edge of the orchard and the creek drainingthe site ranged from approximately 50–80 m at the cherry orchardand 15–40 m at the apple orchard.

In this environment, like many Mediterranean environments,the creeks are not flowing continuously, even during the wintermonths. Auto-samplers (Model 3700, Isco, Nebraska, USA) col-lected water samples at the field edge on a flow-weighted basisfrom two creeks draining an apple and cherry orchard. The auto-samplers were programmed to take a water sample (1 L) after adesignated volume of water had flowed. This ensured that repre-sentative samples were collected through the whole runoff event.Generally, runoff started at both sites around late April to earlyMay, which is the end of autumn. Since the volume of the flowevents at the beginning of the season was considerably less thanlater in the season the auto-samplers were initially programmedto collect water after 50 kL had flowed but later in winter, whenrainfall and runoff became more frequent and events were largerin volume, the frequency of water collection was changed to sam-ple after 5000 kL had flowed at the apple orchard and 1000 kL atthe smaller catchment of the cherry orchard.

All sites were also equipped with an Odyssey logging capac-itance probe (Dataflow Systems Pvt Ltd., Christchurch, NZ) tomeasure water flow and these data were used to determine loadsof the contaminants being transported off-site. The samples werestored at 4 ◦C for a maximum of two weeks until they were analysedfor pesticides. A separate aliquot was retained for measurement oftotal suspended sediment (TSS) by the standard method (APHA,AWWA, WEF, 2005a). A well mixed sample was filtered througha weighed glass fibre filter and the residue retained on the filterwas dried at 103 ◦C. The increase in weight of the filter repre-sented the total suspended sediment (APHA, AWWA, WEF, 2005a).Total C was determined using the standard method (APHA, AWWA,WEF, 2005b) using a TOC/TN Analyser (Skalar Formacs, Breda, TheNetherlands). Since the inorganic carbonates in these samples werenegligible the carbon measured equated to total organic carbon(TC).

2.2. Selection of pesticides for analysis

Prior to commencing the sampling the apple and cherry grow-ers involved with the study were interviewed about pesticide usageon their farms. The pesticide data and environmental information(including rainfall, irrigation volumes, slope etc.) about each sitewere utilised in the risk indicator, Pesticide Impact Rating Index

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(PIRI) developed by Kookana et al. (2005), to determine the like-lihood of off-site transport of the pesticides used in the two landuses. Details of the application dates and quantities of pesticidesapplied are given in Oliver et al. (2012b). This data was also usedfor determining which pesticides would be analysed at each site inthe study. Briefly, PIRI is a water quality risk indicator that can beused as an aid in minimising the off-site impacts of pesticides. PIRIis a simple screening tool that can be used interactively to assessthe relative risk of pesticides or cropping systems in terms of theirpotential impact on surface water or on groundwater quality andecosystem health. For a more detailed explanation of PIRI refer towww.csiro.au/piri.

2.3. Water sample extraction

Water samples were analysed for pesticides as both unfil-tered (i.e. total load composed of chemicals in solution and thoseattached to particulate material), and filtered samples that hadpassed through a 1.2-�m glass fibre filter (Whatman Int. Ltd., Maid-stone, UK). The proportion determined to be in association withcolloidal material (>1.2-�m) was determined by difference. As the“dissolved” proportions were prepared by filtration, the term “dis-solved” in this paper refers only to materials that passed throughthe 1.2-�m filter and does not imply that all materials in the fil-trate were necessarily in solution. Haygarth et al. (1997) showedthat, in the case of phosphorus (P), a large proportion of P in fil-trates of <0.45 �m was associated with colloids and particles of>1000 molecular weight.

In the literature there are a wide range of mesh sizes usedto filter water samples for both nutrient and pesticide analyses,ranging from 1.2 �m to 0.2 �m. In this study the filtered sam-ples were processed after TSS measurements were made since itwas deemed that the pesticides associated with very fine parti-cles (1.2 �m) would not be expected, under field conditions, tobe trapped by grassed waterways or buffer strips, and would beexpected to remain in suspension. Losses of any of the pesticideson the glass fibre filter were determined by filtering a stock solu-tion of known concentration (1 mg L−1) of each individual pesticidethrough the filter. No pesticides losses on the glass fibre filter wereobserved.

For extraction of pesticides, the unfiltered and filtered sampleswere loaded onto C18 solid phase extraction (SPE) cartridges(Extract-Clean C18 HF, Grace Davison, Deerfield, IL, USA) that werepre-conditioned with two washes with 5 mL methanol. After all thewater had percolated through the SPE cartridges they were driedunder vacuum for 15 min. Then two washes of solvent (2.5 mL)were used to elute the pesticide from the SPE cartridge. Theeluting solvent was dichloromethane for chlorpyrifos (0,0-diethyl0-3,5,6-trichloro-2-pyridyl phosphorothioate), acetonitrile forcarbaryl (1-naphthyl methylcarbamate), azinphos methyl (S-(3,4-dihydro-4-oxobenzo[d]-[1,2,3]-triazin-3-ylmethyl) 0,0-diethylphosphorodithioate) and fenarimol ((±)-2,4′-dichloro-�-(pyrimidin-5-yl)benzhydryl alcohol), and acetone for penconazole(1-(2,4-dichloro-�-propylphenethyl)-1H-1,2,4-triazole),bupirimate (5-butyl-2-ethylamino-6-methylpyrimidin-4-yldimethylsulfamate), procymidone (N-(3,5-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide), propiconazole((±)-1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl]-1H-1,2,4-triazole) and pirimicarb(2-dimethylamino-5,6-dimethylpyrimidin-4-yl dimethycar-bamate). Spiked water samples, using high purity water andfield-collected water containing sediment, were run in triplicatewith every batch of water analyses to test the recovery of thepesticides from the SPE cartridge. The average recoveries from theSPE cartridges were almost the same for both matrices. Averagerecoveries (and the number of spiked samples tested) for the

compounds were 97 ± 13% for carbaryl (n = 33), 97 ± 10% for azin-phos methyl (n = 24), 97 ± 8% for fenarimol (n = 48), 111 ± 11% forbupirimate (n = 18), 108 ± 16% for penconazole (n = 30), 74 ± 14%for chlorpyrifos (n = 27), 112 ± 11% for procymidone (n = 48),65 ± 16% for pirimicarb (n = 24) and 111 ± 35% for propiconazole(n = 18).

2.4. Pesticide analysis

The concentrations of chlorpyrifos, and compounds being ana-lysed in water from the cherry growing site were determined usinga gas chromatograph (model 6890) interfaced with a mass spec-trometer (model 5973) (GC–MS) (Agilent, Santa Clara, CA, USA). A30 m DB-5MS column (0.25 mm ID and 0.25-�m film thickness)(J&W Scientific, Folson, CA) was used for separation of the com-pounds with a GC oven temperature programmed at 75 ◦C for 3 min,ramped at 25 ◦C min−1 to 180 ◦C, and then ramping up to 260 ◦C at arate of 5 ◦C min−1 and held at this temperature until the completerun time of 28 min. Helium was used as the carrier gas at a lin-ear flow rate of 0.5 mL min−1 using pulsed splitless injection modewith a splitless inlet liner. The compounds were identified basedon retention times and mass spectra obtained using MS operatedin selected ion monitoring (SIM) in electron impact (EI) ionisa-tion mode with an ionisation voltage of 70 eV. The retention timesfor each compound were: chlorpyrifos 12.0 min, propiconazole18.9 min, penconazole 13.1 min, procymidone 15.1 min, pirimicarb11.8 min, and bupirimate 15.0 min. The detection limits for thecompounds in the original water samples were 0.02 �g L−1 forchlorpyrifos, 0.04 �g L−1 for propiconazole, 0.02 �g L−1 for pro-cymidone, 0.02 �g L−1 for pirimicarb, 0.33 �g L−1 for bupirimateand 0.04 �g L−1 for penconazole.

Analysis of compounds used in the apple orchard were deter-mined using a high performance liquid chromatograph (HPLC)(model 1100, Agilent, CA, USA) equipped with a quaternary pump,a photodiode array detector, and an auto-sampler. The operat-ing conditions were Apollo C18 column (250 mm × 4.6 mm ID,5-�m particle size) (Alltech, KY, USA); isocratic mobile phase 75:25acetonitrile:water; flow rate 1 mL min−1; an injection volume of20 �L; a UV–Vis detector set at a wavelength of 220 nm. The reten-tion times were carbaryl 4.1 min, azinphos methyl 5.0 min andfenarimol 5.6 min. The detection limits for the compounds in theoriginal water samples were carbaryl 0.2 �g L−1, azinphos methyl0.08 �g L−1 and fenarimol 0.08 �g L−1.

3. Results and discussion

3.1. Pesticides moving predominantly in the dissolved phase(<1.2 �m)

Among the fungicides monitored in this study, fenarimol, pen-conazole and bupirimate were found to move predominantly in thedissolved phase for all runoff events irrespective of the size or dura-tion of the runoff event. The average proportion of fenarimol in thedissolved (<1.2 �m) phase ranged from 75 to 100% for all eventsexcept in late July to early August 2008 when the average amountin the dissolved phase was only 63%. An example of fenarimol dis-tribution during several runoff events is shown in Fig. 1a. Similarly,>65% of penconazole was found to move off-site in the dissolvedphase in 2008 and 2009 (Fig. 1b). Bupirimate, which was detectedat concentrations above the detection limit only in 2009, was alsofound to move off-site predominantly (approximately >60%) in thedissolved phase (data not shown).

In the first runoff event in 2007 (April 28) the pirimicarb (aninsecticide) concentration remained quite high (0.7–1.0 �g L−1) forthe duration of the event before declining to below detection limit(<0.2 �g L−1) in later events. In this event approximately >90% of

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Fig. 1. Distribution of (a) fenarimol between the dissolved (<1.2 �m) and particulate (>1.2 �m) phases in water samples moving off-site from the apple orchard from lateApril to early June 2007; (b) penconazole between the dissolved (<1.2 �m) and particulate (>1.2 �m) phases in water samples moving off-site from the apple orchard fromearly to mid July 2009; and (c) pirimicarb between the dissolved (<1.2 �m) and particulate (>1.2 �m) phases in water samples moving off-site from the cherry orchard inrunoff events from early July to early August 2008. TSS (mg L−1) concentration at each sampling time and Australian drinking water guideline (ADWG) (1 �g L−1) for fenarimolare indicated. Separate but consecutive runoff events are indicated on the figure.

the pirimicarb was in the dissolved (<1.2 �m) fraction. Similarly,in 2008 pirimicarb moved off-site predominantly in the dissolvedphase with the average proportion in the dissolved phase for eachrunoff event being >80% (Fig. 1c). Pirimicarb was not detected asfrequently in 2009 as in the other two years but in June 2009 theaverage proportion in the dissolved phase was 67%. Among otherinsecticides, carbaryl was also detected in surface water from theapple orchard in 2008 and 2009 and generally it was found to movepredominantly (>80%) in the dissolved (<1.2 �m) fraction (data notshown). The exception to this was the first runoff event in mid April2009 where the amount moving in the dissolved phase ranged from5 to 62% (data not shown). Generally, the total amount of pesticidemoving off-site from both orchards was <0.5% of the total massof active ingredient applied. The exception to this was fenarimolwhere the annual load transported off-site ranged from 0.54 to 2.1%of the total mass of active ingredient applied. More details of thetotal loads of pesticides transported off-site each year are given inOliver et al. (2012b).

The chemicals that move predominantly in a dissolved(<1.2 �m) phase would be expected to be more readily availableto aquatic organisms compared with those that are attached tocolloidal material. Subsequently, of those detected in this studymoving predominantly in a dissolved (<1.2 �m) phase, the insecti-cides (namely carbaryl and pirimicarb) would be expected to posea greater risk to invertebrates based on the LC50 values for thesechemicals when tested against Daphnia sp. (0.006 and 0.017 mg L−1,respectively). By contrast, the fungicides, fenarimol and bupiri-mate, have considerably higher LC50 values for Daphnia sp. (5.1and >3.41 mg L−1, respectively), and would pose a lesser risk toinvertebrates.

There was a positive, albeit weak, relationship between the pir-imicarb concentrations in water samples from the cherry orchardand TC concentrations (R2 = 0.17) when one high TC value (1% ofdata) was deleted but the majority of the pirimicarb detectionswere very close to the detection limit (data not shown). There wasa similar positive but weak relationship between the penconazole

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Fig. 2. Relationship between dissolved (<1.2 �m) fenarimol concentration and dis-solved TC concentration in water samples from the apple orchard from 2009 only.

data (which was only detected in 2009) and TC (R2 = 0.12, data notshown). Much stronger positive relationships were found for fena-rimol when regressed against TC (R2 = 0.23, data not shown). Whenspecific years were considered the regressions were even stronger.For the regression of fenarimol concentration and dissolved TC con-centration the R2 values were 0.53 and 0.54 for the 2007 and 2009data, respectively (Fig. 2).

3.2. Pesticides moving predominantly in association withparticulate material (>1.2 �m)

There were fewer pesticides in this study found to move pre-dominantly with particulate material (>1.2 �m). The fungicide,propiconazole, was only detected in runoff samples in the April 28and early July events in 2007 but the majority (70–90%) was asso-ciated with particulate material (>1.2 �m) (Fig. 3). Wu et al. (2003)studied the sorbtivity of propiconazole with different particle sizefractions of agricultural runoff material. They noted that whensediment concentration in runoff water was as low as 200 mg L−1

propiconazole was mainly be in a dissolved form. However in ourstudy the TSS concentration in the water samples where propicona-zole was detected, were generally below 200 mg L−1 (Fig. 3) butpropiconazole was found predominantly in the particulate phase(>1.2 �m).

The fungicide, procymidone, was detected at relatively high con-centrations (0.4 �g L−1) in the first sample collected on April 28

Fig. 3. Distribution of propiconazole between the dissolved (<1.2 �m) and particu-late (>1.2 �m) phases in water samples moving off-site from the cherry orchard inrunoff events from April to July 2007. TSS (mg L−1) concentration at each samplingtime and Australian drinking water guideline (ADWG) (0.1 �g L−1) for propiconazoleare indicated. Separate but consecutive runoff events are indicated on the figure.

Fig. 4. Distribution of chlorpyrifos between the dissolved (<1.2 �m) and particulate(>1.2 �m) phases in water samples moving off-site from the apple orchard in runoffevents from April to June 2007. TSS (mg L−1) concentration at each sampling time andAustralian freshwater trigger value for protection of 95% of species (AFWTV∼95%)(0.01 �g L−1) for chlorpyrifos are indicated. Separate but consecutive runoff eventsare indicated on the figure.

2007 and approximately 60–70% of procymidone was in the par-ticulate (>1.2 �m) fraction (data not shown). The concentrationquickly decreased to less than the detection limit (0.02 �g L−1)in subsequent water samples collected from that runoff event.However, the mode of transport of procymidone was not consis-tent across years. In 2008 and 2009 procymidone was detectedover a longer time period and in these years a greater proportion(>80%) of procymidone was detected moving in the dissolved phase(<1.2 �m) (data not shown). Dabrowski et al. (2002) found procymi-done at very high concentrations in runoff water only in samplescollected from a catchment with a mediterranean climate similarto that of this study site.

A strong relationship between the concentration moving off-site and the TSS concentration was expected for chemicals thatwere transported predominantly in the particulate (>1.2 �m) frac-tion, namely procymidone in 2007 and propiconazole in drainagewater from the cherry orchard. However, there was no significantrelationship between procymidone or propiconazole concentrationand TSS concentration when the unfiltered (total) or particulate(>1.2 �m) fraction was considered. In fact, regressions of pesticideconcentrations as the unfiltered (total) concentration or as the por-tion in the dissolved (<1.2 �m) or particulate (>1.2 �m) fractionagainst TSS concentration found very few significant relationshipsfor any of the pesticides detected at either the apple or the cherryorchards. A positive significant (P < 0.05) relationship between con-centration in the particulate fraction and TSS concentration wasobserved only for the 2008 penconazole data (R2 = 0.24) from theapple orchard and only when two high TSS values (2% of total TSSvalues) had been deleted (data not shown). Of the pesticides mon-itored in this study penconazole had the third highest Koc value(2500 L kg−1, Table 1) but a higher proportion (>65%) was gener-ally transported off-site in the dissolved phase. This data suggeststhat TSS could not be used as a surrogate for monitoring of off-sitetransport of pesticides.

3.3. Pesticides moving in no consistent pattern

In this study the partitioning of chlorpyrifos into differentfractions was less consistent. For example, the proportion of chlor-pyrifos that was measured in the dissolved (<1.2 �m) phase wasvariable and ranged from 26.4% in a runoff event from September11 to October 6, 2008 to 87.1% in a runoff event in July 31 to August10, 2007. In 2007 the dissolved fraction was generally highest atthe commencement of the runoff event (e.g. April 28 and May31, 2007 events, Fig. 4) and as the event proceeded the fraction

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Table 1Selected properties of chemicals detected in surface water.

Chemicals detected Half-life (days)a Koc (L kg−1)b Solubility in water(mg L−1) (20 C)a

Wauchope (1978)criteriac

Goss and Wauchope(1990) criteriae

Main mode oftransport in this study

Carbaryl (7–28) 17.5 211 120 Wd Lf WChlorpyrifos (7–56) 31.5 (1250–12,600) 6925 1.4 Sd Hf W/SPirimicarb (7–234) 120.5 86 3000 W L WAzinphos methyl 24.5 1000 28 W L WFenarimol (14–30) 72 (500–992) 746 13.7 W L WPenconazole (133–343) 238 2205 73 W H WProcymidone (28–84) 56 378 4.5 W H WPropiconazole (40–70) 56 1086 100 W H SBupirimate (35–90) 62.5 1882 22 W L S

a Tomlin (2000).b http://sitem.herts.ac.uk/aeru/iupac/index.htm (accessed 00.05.11).c Primary transport by sediment (S) if water solubility < 1 mg L−1 (Wauchope, 1978).d S = transport by sediment; W = transport in aqueous phase based on Wauchope (1978).e High potential for particle bound transport is DT 50 ≥ 40 d and Koc ≥ 1000 (Goss and Wauchope, 1990).f H = high potential for particle bound transport; L = low potential for particle bound transport based on Goss and Wauchope (1990).

being transported off-site in the particulate phase (>1.2 �m)increased. In later events in the season (e.g. July 29, 2007, data notshown) a greater proportion of chlorpyrifos was transported inthe dissolved phase (<1.2 �m). This observation however was notalways consistent between years. In an event later in 2008 chlor-pyrifos was transported off-site predominantly in the particulatephase (August to October 2008, Fig. 5). Pedersen et al. (2006) whomonitored organophosphorus insecticide (including chlorpyrifos)concentrations in surface runoff from agricultural and residentialsites also found these chemicals present in the dissolved phase(<0.7 �m) from all sites during each event sampled. By contrast,Dabrowski et al. (2002) found chlorpyrifos in both runoff waterand in particle-associated form in surface water draining fromintensive farming areas in South Africa. The detection of chlor-pyrifos in association with particulate material indicates thatchlorpyrifos poses a potential hazard to aquatic and sedimentdwelling organisms. Chlorpyrifos has relatively low LC50 valuesfor Rainbow trout (0.029 mg L−1), algae (0.4 mg L−1) and Daphniasp. (0.0017 mg L−1), which indicates that this chemical poses quitea significant risk to organisms in different trophic levels.

A significant exponential inverse relationship (P < 0.05) wasfound between the chlorpyrifos concentration of the unfiltered(total) and the dissolved (<1.2 �m) fraction and TSS concentra-tion (Fig. 6). It was not possible to measure the composition of theTSS fraction but the relationship between pesticides transportedoff-site and the total carbon content are discussed in Oliver et al.(2012b). Given the variation in the proportion of chlorpyrifos thatwas transported in the dissolved compared to particulate phases

Fig. 5. Distribution of chlorpyrifos between the dissolved (<1.2 �m) and particulate(>1.2 �m) phases in water samples moving off-site from the apple orchard in runoffevents mid August to early October 2008. TSS (mg L−1) concentrations at each sam-pling time are indicated. Separate but consecutive runoff events are indicated onthe figure.

throughout the runoff events over the three years, this result mostlikely reflects the observations of Leonard’s (1990) that the factorsthat determine whether a pesticide is transported primarily dis-solved in water or attached to sediment depends on the Kd valueof the pesticide and sediment concentrations. Leonard (1990) sug-gested that when sediment concentrations are low, the dominantform in which pesticides are transported is in solution, even forstrongly sorbed pesticides, because volumes of runoff water greatlyoutweigh masses of sediment. Conversely, when sediment concen-trations are high transport of pesticides associated with sedimentwill be significant even for those pesticides with intermediate Kd.Consequently, it would be expected that there should be an inverserelationship between sediment concentration and pesticide con-centration even for those pesticides with a low to intermediateKd. However, in the present study, the generalised relationship ofLeonard (1990) was only observed for chlorpyrifos which had thesecond highest Koc value (Table 1) of those pesticides detected, andnot seen for the other pesticides studied.

Wauchope (1978) reviewed pesticide content of surface waterdraining agricultural fields and found only those pesticides withwater solubilities <1 mg L−1 were transported primarily with sed-iment. Of the pesticides monitored in this study chlorpyrifos(solubility: 1.4 mg L−1, Table 1), was the only chemical to approxi-mately fulfil the Wauchope (1978) criteria. Chlorpyrifos was foundon occasions to be transported off-site predominantly with partic-ulate material but this was not a consistent trend. Furthermore,propiconazole (solubility: 100 mg L−1, Table 1), was transportedoff-site predominantly with particulate material. Brown et al.(1995) studied isoproturon, mecoprop, fonofos and trifluralin

Fig. 6. Relationship between dissolved (<1.2 �m) chlorpyrifos concentration andTSS concentration in water samples from the apple orchard collected in 2007–2009.

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Fig. 7. Relationship between average proportion (%) of each pesticide monitored inthe dissolved phase for each runoff event over the three year study and the watersolubility (mg L−1) of each pesticide.

movement on plots and only trifluralin (water solubility < 1 mg L−1)moved predominantly in association with sediment.

A Norwegian assessment of three OECD risk indicators classi-fied pesticides with high, medium and low potential for particlebound transport as 0.5, 0.3 and 0.1%, respectively, based on acategorisation of potential of pesticides to be transported off-site by Goss and Wauchope (1990). In this study the amount ofpesticide transported off-site was less than 0.5% for all chem-icals detected in runoff in 2007 except fenarimol. The systemdeveloped by Goss and Wauchope (1990) states potential forparticle-bound transport is high if DT50 > 40 days and Koc > 1000.The half-life for fenarimol is 14–130 days (average 79 days) andthe Koc is 500–992 L kg−1 (Tomlin, 2000). Therefore, out of allthe pesticides detected in this study, only chlorpyrifos, pencona-zole, procymidone and propiconazole would be expected to havea high potential to be transported associated with particulatematerial based on the criteria of Goss and Wauchope (1990).However, we found that propiconazole was the only pesticide tomove off-site predominantly associated with particulate materialconsistent with the behaviour predicted by Goss and Wauchope(1990).

3.4. Relationship between pesticide characteristics andproportion moving off-site

In many situations there is not detailed hydrological informa-tion for a site and it is not always easy (or inexpensive) to obtain thisinformation. Consequently, many first tier assessments of the like-lihood of off-site transport of pesticides rely upon physicochemicalproperties of pesticides. Physicochemical properties of pesticidessuch as water solubility, Koc or Kow, may be useful for predictinggeneral transport behaviour of pesticides in the environment andspecifically which fraction of the pesticide is likely to dominateoff-site transport of pesticides. Wauchope (1978) found a simpleS-curve fitted a plot of the ranges of fractions of pesticides lost inthe dissolved phase of runoff reported in the literature with solu-bility. In order to assess this prediction the relationship betweenthese pesticide characteristics and the average proportion (%) ofeach pesticide in the dissolved (<1.2 �m) fraction for each eventwere determined. Although there was a general trend of a higheraverage percentage of pesticide being transported off-site in thedissolved (<1.2 �m) fraction with increasing water solubility of thepesticides monitored this relationship broke down when propi-conazole and pirimicarb were included (Fig. 7). The range of average% dissolved fraction moving off-site for carbaryl (water solubility120 mg L−1, Table 1) was 35–100%, and for penconazole (water sol-ubility 73 mg L−1, Table 1) was 7–100%. However, for penconazoleand carbaryl there was only one event where the average amount(%) in the dissolved fraction was low and for the rest of the runoff

events it was >95% for carbaryl and >70% for penconazole. However,this general trend of “high” average proportion (%) transportedoff-site in the dissolved fraction for pesticides with high water sol-ubilities however did not hold for pirimicarb which had the highestwater solubility of the pesticides monitored (3000 mg L−1, Table 1).The range of average amount transported in the dissolved frac-tion for pirimicarb was 36–100%, although for the majority of therunoff events the average proportion in the dissolved phase was>60%.

For those pesticides with a low water solubility there was aneven wider range for the proportion in the dissolved phase. Forexample, the range of average proportion in the dissolved phase forchlorpyrifos, which has a water solubility of 1.4 mg L−1 (Table 1),was 26–87% over 23 events. A similar, but opposite, relationshipwas observed for the pesticides studied and Kow values (data notshown). There was also no relationship between average propor-tion in the dissolved phase and soil half-life. This would suggest thatother factors such as timing of sprays in relation to rainfall events,intensity of the rainfall event, duration of the rainfall event, etc.have a large impact on pesticide transport that make predictionsof likelihood of off-site transport based on pesticide characteris-tics very difficult. This data demonstrates that it is not possible touse simple surrogates to predict the likelihood of off-site transportunder field conditions.

3.5. Implications for management strategies

The majority of studies in the literature investigating strategiesto minimise off-site transport of pesticides have focussed on bufferstrips or interception ponds. Schulz (2004) argued that heavy rain-fall events causing storm runoff are always associated with theproduction of very large volumes of water in a short time, which inmany cases will be retained by any sort of widely employed bufferstrip. A summary of studies investigating buffer strips noted thatthe efficiency of buffer strips depends on the nature of the runoffevent (Reichenberger et al., 2007). In some studies it was found thatsome smaller runoff flows (and associated pesticides) infiltratedcompletely, whereas some large runoff flows were not significantlyretained by the strips (Arora et al., 1996). Reichenberger et al. (2007)concluded that the effectiveness of grassed buffer strips located atthe edges of fields in decreasing pesticide runoff is variable andthis variability cannot be explained by strip width alone. The effec-tiveness of buffer strips also depends on the ability of the bufferto decrease the rate of flow of water to allow both the settling ofany suspended sediment, which may have pesticides attached, andthe sorption of any dissolved pesticides to soil. In this study thealley ways between the trees and the section between the edgeof the orchard and the creek draining both sites (approximately50–80 m at the cherry orchard and 15–40 m at the apple orchard)was grassed. Despite a grassed buffer being maintained at both sitesthe authors suspect that there was insufficient residence time forthe pesticides to sorb and be removed from solution. However,there were no measurements of water transit times through thebuffer regions to quantify this and any increases in buffer widthwould have economic implications for growers since more landwould be taken out of production.

There have been very few studies on the effectiveness of con-structed wetlands to decrease the concentration of pesticides inwater and the majority of studies have dealt with strongly sorb-ing insecticides with a strong tendency to adsorb to macrophytes,suspended particles or bed sediment (Moore et al., 2000; Schulzand Peall, 2001; Scott et al., 1999). For chemicals that move pre-dominantly in a dissolved phase, such as fenarimol, bupirimate,and pirimicarb, the effectiveness of buffer strips or sedimentationponds for removing these pesticides from water may be limited andalternative management strategies may need to be investigated.

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4. Conclusions

The majority of fungicides and insecticides monitored in thisstudy were found to move off-site in the dissolved (<1.2 �m)phase. Only propiconazole moved off-site predominantly (70–90%)in association with particulate (>1.2 �m) material. The form inwhich chlorpyrifos moved varied between events and during anevent. There were occasions when the predominant form was inassociation with particulate (>1.2 �m) material but as the eventprogressed or in later events during winter chlorpyrifos was foundto move predominantly in the dissolved phase (<1.2 �m). Therewas no relationship between average proportion in the dissolved(<1.2 �m) phase during a runoff event and any of the pesticidecharacteristics considered. Although there was a general trend ofpesticides with a water solubility > 15 mg L−1 moving, on average(>60%), in the dissolved (<1.2 �m) phase, propiconazole (water sol-ubility 100 mg L−1) did not conform to this generalisation. Thissuggests that offsite transport of pesticides is governed by com-plex biological and hydrological interactions and the use of simplephysicochemical properties as surrogates for predicting offsitetransport may not be reliable. The mode of transport of pesticideshas significance for the effectiveness of management strategies andthis data suggests that the use of buffer strips, which are com-monly suggested to minimise transport, may have limited use forpesticides used in apple and cherry production in Australia.

Acknowledgments

The financial support of Australian Centre for InternationalAgricultural Research (ACIAR), National Landcare Program (NLP)and Centre for Natural Resource Management for this study aregratefully acknowledged. The growers who participated in thisproject are also thanked for their generosity. The assistance ofCSIRO staff who reviewed the article before submission is gratefullyappreciated.

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