Banks, John

Stark, John D

English

University of Washington: UW Tacoma Digital Commons

University of Washington TacomaUW Tacoma Digital CommonsSIAS Faculty Publications School of Interdisciplinary Arts and Sciences11-2001"Selective" Pesticides: Are They Less Hazardous tothe Environment?John D. StarkWashington State UniversityJohn BanksUniversity of Washington Tacoma, jebanks@csumb.eduFollow this and additional works at: https://digitalcommons.tacoma.uw.edu/ias_pubPart of the Environmental Health and Protection Commons, and the Life Sciences CommonsThis Article is brought to you for free and open access by the School of Interdisciplinary Arts and Sciences at UW Tacoma Digital Commons. It hasbeen accepted for inclusion in SIAS Faculty Publications by an authorized administrator of UW Tacoma Digital Commons.Recommended CitationStark, John D. and Banks, John, ""Selective" Pesticides: Are They Less Hazardous to the Environment?" (2001). SIAS FacultyPublications. 4.https://digitalcommons.tacoma.uw.edu/ias_pub/4980 BioScience  •  November 2001 / Vol. 51 No. 11ForumFor half a century, scientists and the public have beenwell aware of the risk posed by pesticides to humansand the environment. Worldwide concern about pesticideresidues on food and in drinking water has led to legislativeefforts to restrict the use of traditional, broad-spectrumpesticides. In the United States, the Food Quality ProtectionAct (Public Law 104-170), passed by Congress in 1996, ef-fectively mandates a severe reduction in the use of many suchpesticides for a wide range of agricultural uses. The princi-pal rationale for restricting the use of many of these chem-icals is to protect consumers, especially children, who arejudged to be more susceptible to the effects of pesticides(NRC 1993, Goldman 1998).For their part, in anticipation of the loss of many widelyused organophosphorus and carbamate insecticides, pesticideproducers have developed a suite of new biorational pesticidesdesigned to target only select organisms. These new productsare typically termed selective based on the results of simple lab-oratory dose–response trials with target and nontarget speciesto determine LD50, the dose of a chemical that kills 50% ofthe population tested (LD = “lethal dose”). There is increas-ing evidence that many nontarget species are affected by sev-eral of these chemicals in ways that are often surprising andunpredictable (Banken and Stark 1998, Boyd and Boethel1998, Losey et al. 1999, Smith and Krischik 1999).Unfortunately, little effort has been directed toward de-veloping alternative measures of toxicity of these new chem-icals and then using them in risk assessment. Thus, we set outto quantify the extent to which these new chemicals may belethal to nontarget organisms. We compared the toxicity ofsix new selective insecticides to the toxicity of a widely used,broad-spectrum, representative organophosphorus insecti-cide (diazinon). In addition, we used two toxicological end-points in a simplistic hazard assessment exercise. The first haz-ard assessment was performed using the traditional LC50method (LC50 is a statistical estimate of the concentration,in a medium such as water, that kills 50% of the population);the second was done using a measure of population growthrate and estimating the concentration that caused populationextinction.We focused on insecticides in this study because they rep-resent a larger threat to biological communities and the en-vironment than fungicides and herbicides (Croft 1990). Wechose to assess the impacts of insecticides on an aquaticspecies, the Cladoceran Daphnia pulex (Walthall and Stark1998). This animal is widely studied and is commonly usedas an indicator species for environmental contaminants(USEPA 1991).We developed acute (48 hours) lethal concentration esti-mates (LC50) and a 10-day measure of population growth rate,the instantaneous rate of increase (Walthall and Stark 1997)for the following insecticides: diazinon, spinosad, Neemix 4.5,phloxine B, Fulfill, Aphistar, and Actara (Figure 1). All ofthese insecticides are relatively new, except for diazinon, awidely used organophosphorous neurotoxin that is a commoncontaminant found in aquatic systems (Gilliom et al. 1999,USGS 1999).Extinction concentrations were generated by regressionanalysis on population growth rate–concentration data (Fig-ure 1), in which the extinction threshold was defined as agrowth rate of –0.01. Substitution of the extinction thresh-old into regression equations resulted in a correspondingextinction concentration (x-axis intercept of regression line)for each chemical tested.Because environmental concentration data for the newselective insecticides are limited, we modified a hazard as-sessment technique geared toward direct applications ofchemicals into a body of water (AAFC 1993). The techniqueinvolves the use of the expected environmental concentrationJohn D. Stark (e-mail: stark@puyallup.wsu.edu ) is a professor in theEcotoxicology Program, Department of Entomology,Washington StateUniversity, Puyallup, WA 98371-4998. John E. Banks is an assistantprofessor in Interdisciplinary Arts and Sciences, University of Wash-ington, Tacoma, WA 98402-3100. © 2000 American Institute of Biological Sciences.“Selective” Pesticides: AreThey Less Hazardous to theEnvironment? JOHN D. STARK AND JOHN E. BANKSNovember 2001 / Vol. 51 No. 11 •  BioScience 981Forum(EEC), which is defined as the concentration of pesticide in150 liters of water after direct application on a forest at themaximum application rate. To develop the EEC, we used theaverage foliar application rate (Table 1) instead of the max-imum rate. To determine the average, we calculated the meanof the lowest and highest recommended application ratesgiven by manufacturers or listed in CropProtection Reference (1998). EECs used inthe hazard assessments are shown inTable 1. Hazard quotients were gener-ated by dividing the EEC by the LC50 orpopulation extinction concentration.Hazard quotients greater than 1 indicatethat a chemical may cause damage to anecosystem (Suter 1993).Acute LC50 assessments indicated thatall the new insecticides were significantlyless toxic than diazinon (p < 0.05) (Table2). Hazard assessment based on the LC50suggests that none of the new insecti-cides posed a hazard to D. pulex except forthe acetylcholinesterase inhibitor Aphis-tar (Table 3). In contrast, hazard assess-ment based on a concentration thatwould cause extinction indicated thatmost of the new insecticides pose a haz-ard to D. pulex (Table 3). Actara was bor-derline with a hazard quotient of 1, andphloxine B was far below the environ-mental hazard threshold.The traditional LC50 measure indi-cated that the least toxic selective insec-ticide was Actara, at approximately 6.6 x104 times less toxic than diazinon (Table2). On the other hand, the extinctionconcentration indicated that Actara was only 22 times less toxicthan diazinon. Hazard quotients generated using two differ-ent toxicological endpoints spanned three orders of magni-tude, varying from 1.5- to 1122-fold (Actara). For some in-secticides, both hazard quotients gave similar results (Aphistarand phloxine b), but for others, huge differences were present(Actara, Fulfill, Neemix, and spinosad; Table 3).Population extinction concentrations for the new selectiveinsecticides ranged from 3 to 406 times less than diazinon.With such variable patterns of relative toxicity, it is evident thatgeneralizations about the toxicity of the new generation of se-lective pesticides may be premature.The differences we found between LC50 and population extinction–based risk assessments serve as a cautionary talefor those establishing toxicological protocols for these newchemicals. Furthermore, they highlight the need to morecarefully screen the full range of effects that chemicals mayhave at both the individual and population levels. While themore simplistic (and standard) LC50 analysis indicates that thenew insecticides pose little hazard to D. pulex, the populationextinction analysis reveals a substantially greater overall men-ace. Field studies have further indicated that the ability to pre-dict how organisms will respond to selective pesticides be-comes even more challenging in the context of biologicalcommunities, including target and nontarget organisms alongwith their suite of natural enemies (Banks and Stark 1998).Table 1. Average foliar application rates and expectedenvironmental concentrations of insecticidesevaluated in the hazard assessments.Average foliarapplication rate (mg active ingredient EEC1Chemical per m2) (mg per l)Diazinon 237.8 1.585Actara 6 0.040Aphistar 0.028 0.186Fulfill 21 0.140Neemix 5 0.033Phloxine B 14.6 0.097Spinosad 0.2 0.0681. EEC is the concentration of pesticide in 150 l of water after adirect over spray of a forest at the average foliar application rate.Comparison of instantaneous rate of increase for Daphnia pulex exposed todiazinon and a suite of selective pesticides. Instantaneous rates of increase/d is ameasure of population growth rate 10 days after the start of the experiment (seeWalthall and Stark 1997 for details).(µg/l)982 BioScience  •  November 2001 / Vol. 51 No. 11AcknowledgmentsWe thank Peter Kareiva (National Oceanic and AtmosphericAdministration, Seattle) for his valuable comments and sug-gestions regarding the manuscript. We also thank Grace Jack,William Walthall, and Barbara Wood for help in collectingdata.References cited[AAFC] Agriculture and Agri-Food Canada. 1993. Registration guidelinesfor microbial pest control agents. Ottawa, Ontario: Plant Industry Di-rectorate, AAFC. Bulletin Pro93-04.Banken JAO, Stark JD. 1998. Multiple routes of pesticide exposure and therisk of pesticides to biological controls: A study of neem and the seven-spot lady beetle, Coccinella septempunctata L. Journal of Economic En-tomology 91: 1–6.Banks JE, Stark JD. 1998. What is ecotoxicology? An ad-hoc grab bag or aninterdisciplinary science? Integrative Biology 1: 195–204.Boyd ML, Boethel DJ. 1998. Residual toxicity of selected insecticides to Het-eropteran predaceous species (Heteroptera: Lygaeidae, Nabidae, Pen-tatomidae) on soybean. Environmental Entomology 27: 154–160.Croft BA. 1990.Arthropod Biological Control Agents and Pesticides. New York:John Wiley and Sons.Crop Protection Reference, 14th ed. 1998. New York: C&P Press.Gilliom RJ, Barbash JE, Kolpin DW, Larson SJ. 1999. Testing water qualityfor pesticide pollution. Environmental Science and Technology 4:164a–169a.Goldman LR. 1998. Linking research and policy to ensure children’s envi-ronmental health. Environmental Health Perspectives 106 (supplement3): 857–862.Losey JE, Rayor LS, Carter ME. 1999. Transgenic pollen harms monarch lar-vae. Nature 369: 214–216 .[NRC] National Research Council. 1993. Pesticides in the diets of infants andchildren. Washington (DC): National Academy Press.Smith SF, Krischik VA. 1999. Effects of systemic Imidacloprid on Coleomegillamaculata (Coleoptera: Coccinellidae). Environmental Entomology 28:1189–1195.Suter, GW II. 1993. Ecological Risk Assessment. Boca Raton (FL): Lewis Pub-lishers.[USEPA] US Environmental Protection Agency. 1991. Methods for measuringthe acute toxicity of effluents and receiving waters to freshwater and ma-rine organisms. Cincinnati (OH): USEPA. EPA/600/4-90/027.[USGS] US Geological Survey. 1999. The quality of our nation’s waters:Nutrients in pesticides. Reston (VA): USGS. Circular no. 1225.Walthall WK, Stark JD. 1997. Comparison of two population-level ecotox-icological endpoints: The intrinsic (rm) and instantaneous (ri) rates ofincrease. Environmental Toxicology and Chemistry 16: 1068–1073.———. 1998. The acute and chronic toxicity of two xanthene dyes, fluoresceinsodium salt and phloxine B, to Daphnia pulex (Leydig). EnvironmentalPollution 104: 207–215.ForumTable 2. Acute (48h) lethal concentration estimates for Daphniapulex exposed to different insecticides.LC50, with 95% Number fiducial limitsChemical tested Slope + SE (mg per l)Diazinon 210 2.34 ± 0.27 0.00062 (0.00056–0.00070)Actara 100 9.1 ± 2.0 41 (37.6–45.7)Aphistar 125 8.8 ± 1.8 0.053 (0.047–0.057)Fulfill 210 0.72 ± 0.11 0.165 (0.077–0.325)Neemix 100 8.09 ± 1.55 0.680 (0.595–0.748)Phloxine B 320 3.6 ± 0.37 0.423 (0.376–0.477)Spinosad 320 1.01 ± 0.17 0.129 (0.077–0.181)Note: See Walthall and Stark 1997 for the full description of methods of toxicity testing.Table 3. Hazard of insecticides to Daphnia pulex.Extinctionconcentration Hazard quotient based on Hazard quotient Difference in hazard Chemical (mg per liter) population extinction based on LC501 quotients (percentage)Diazinon 0.0016 991.0 2,556 2.58Actara 0.035 1.1 0.00098 1122.45Aphistar 0.035 5.3 3.55 1.49Fulfill 0.005 28.0 0.851 32.90Neemix 0.015 2.2 0.049 44.90Phloxine B 0.65 0.15 0.23 0.65Spinosad 0.007 9.7 0.527 18.411. This assessment takes into account both toxicity and potential exposure based on average spray application rates. Hazard quotients were generated bydividing the expected environmental concentration by LC50 or population extinction measures for each chemical. Hazard quotients equal to or less than 1indicate that the chemical poses a risk.BIOLOGY, Sixth Edition Neil Campbell and Jane Reece 0-8053-6624-5With BIOLOGY, SixthEdition, authors NeilCampbell and Jane Reecehave once again crafted asynthesis of modern biologythat you and your studentscan depend on for clearexplanations, innovativeillustrations, and scientificaccuracy.Please visit www.aw.com/bc/ info/campbell6e for moreinformation.iGenetics is the first integrated text with all text, art, and media created to provide a balanced introduction to genetics. Buildingon the proven strength of Peter J. Russell’sstep-by-step problem-solving approach,iGenetics takes a modern, molecularapproach. 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Selective  Pesticides: Are They Less Hazardous to the Environment?

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Selective Pesticides: Are They Less Hazardous to the Environment?

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