Influence of cypermethrin and fenvalerate on natural soil algal populations

ECOTOXICOUXiY

AND

ENVIRONMENTAL

SAFETY

12,14

1- 145 ( 1986)

Influence of Cypermethrin and Fenvaierate Natural Soil Algal Populations M. MEGHARAJ,

K. VENKATESWARLU,

on

AND A. S. RAO

Department ofBotany, Nagarjuna University, Nagarjuna Nagar-522510.

Andhra Pradesh, India

Received August 7.1985 Two synthetic pyrethroids, cypermethrin and fenvalerate, were assessed for their e5ects on soil algae. Single or two repeated applications of cypermethrin or a single application of fenvalerate to soil at 0.5 to 1.0 kg ha-’ had no inhibitory effect on algal flora. Two applications of fenvalerate, at concentrations of 0.75 to 5 kg ha-‘, resulted in a significant increase in populations of algae. No change in the population size was observed even when either monocrotophos or quinalphos was added between two applications of a pyrethroid, all at the 1.O kg ha-’ level. 0 1986 Academic

Press, Inc.

INTRODUCTION Synthetic pyrethroids, a new class of insecticides, are effective against a wide range of agricultural insect pests (Harris and Tumbull, 1978). Regular prophylactic application of pyrethroids from about 70 days after planting will provide protection against insect damage to many plants (Morton, 1979). Breese and Highwood (1977) reported that cypermethrin application, at 0.12 kg a.i.ha-’ , was most effective in reducing bollworm (Heliothis armigera, Earias spp., and Pectinophora gossypiella) incidence. Cypermethrin was also shown to be effective in controlling rice tungro virus disease and its vector (Satapathy and Anjaneyula, 1984). Fenvalerate has great potential for the control of a wide array of pests in agriculture (Caplan, et al., 1984). Although cypermethrin and fenvalerate have been used extensively on cotton either singly in succession or alternated with organophosphorus insecticides (Anonymous, 1984), there have been no reports concerning the effects of these insecticides on microalgae which are ubiquitous, forming an important component of the soil ecosystem. The present study is, therefore, aimed at evaluating the impact of single or two repeated soil applications of the synthetic pyrethroid insecticides, cypermethrin and fenvalerate, on algal flora.

MATERIALS

AND

METHODS

A black cotton soil collected from a fallow cotton field to a depth of 8 cm was airdried and passed through a 2-mm-mesh sieve before use. Measured characteristics for the soil included pH 7.4 (1: 1.25 soilzwater ratio), organic matter 1.82% (Walkley and Black, 1934), and total nitrogen, 0.044% (Jackson, 1958). Portions (20 g) of the soil sample were taken into test tubes (25 X 150 mm). Aqueous solutions of the commercial formulations of two synthetic pyrethroids, viz., Cyperkil125 EC (125% cypermethrin, 1Y-cyano-3-phenoxyphenyl-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate) and Fenkem 25 EC (~25% fenvalerate, cyano(3-phenoxyphenyl)methyl 4-chloro-a-( 1-methylethyl)benzeneacetate), were applied to the soil samples. 141

0147-6513/86$3.00 Copyright 0 1986 by Academic Fies, Inc. All rights of reproduction in any form reserved.

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Experiment A. These chemicals were applied at concentrations of 5, 7.5, 10, 15, 25, and 50 pg a.i.g.-’ soil (equivalent to 0.5,0.75, 1.0, 1.5,2.5, and 5.0 kg ha-‘, on a dry weight basis). Untreated soil samples served as controls. Finally, all the treatments were maintained at 50% water-holding capacity (WHC) and the tubes were incubated in the laboratory under diffused light at an average temperature of 28 + 4°C. At 15 and 25 days after pyrethroid treatment, the soil samples were withdrawn for the estimation of algae by the most-probable-number (MPN) method as described previously (Muralikrishna and Venkateswarlu, 1984). The predominant algal forms were characterized to the generic level. Experiment B. In another experiment, cypermethrin and fenvalerate were applied twice to the soil samples on Days 0 and 15 at the same concentrations as mentioned above since these insecticides are applied repeatedly at 15&y intervals on cotton. The soil samples were further incubated for 15 and 25 days after the second application of the pyrethroids, and the density and frequency of algae were determined. Experiment C. The soil samples, in yet another experiment, were first treated with a pyrethroid (cypermethrin or fenvalerate) at 1.O and 5.0 kg ha-’ levels. Fifteen days after the pyrethroid application, either Nuvacron 36 EC (-36% monocrotophos; dimethyl(E)-1-methyl-2-methylcarbamoylvinyl phosphate) or Ekalux 25 EC (~25% quinalphos; O,O-diethyl O-quinoxalin-Zyl phosphorothioate) was added at the corresponding level of the pyrethroid. Again, the pyrethroid was applied, at the same concentrations used initially, after 10 days of the organophosphate treatment so that each soil sample received two applications of a pyrethroid alternated with an application of an organophosphorus insecticide. Total viable counts were determined, and dominant algal flora were categorized, after 15 and 25 days of the last application of the pyrethroid. In all cases, lower and upper fiducial limits at a 95% confidence level for each MPN value were calculated using the formula of Fisher and Yates (1963). RESULTS Data on the reaction of soil algae as a result of single or two applications of cypermethrin or fenvalerate are presented in Table 1. Cypermethrin or fenvalerate when added to the soil only once, especially at levels of 0.5 to 1 .O kg ha-‘, did not affect the viable counts of algae. However, algal numbers decreased slightly with increasing concentrations of both pyrethroids. This dose-related inhibition was more pronounced by the end of 25 days after single application. Until 15 days after the second application of either cypermethrin or fenvalerate, the toxic effect on algal populations was almost comparable to that of a single application. But 25 days after two additions of cypermethrin at all the concentrations, there was no remarkable effect on algal flora. Although cypermethrin is short-lived in soils with a half-life of 2 to 4 weeks yielding hydrolytic products (3-(2,2dichlorovinyl)2,2dimethylcyclopropanecarboxylic acid, and 3-phenoxybenzoic acid) under aerobic conditions (Roberts and Standen, 1977), the parent compound and/or the metabolites did not seem to have encouraged or inhibited algal growth. All levels of fenvalerate application resulted in increased population of algae, significantly at the end of 25 days after the second addition. Thus, even with a 1.O kg ha-’ level of fenvalerate application, the increase in the population density of algae was nearly 1 l-fold over the untreated control. Higher levels (1.5 to 5.0 kg ha-‘) also

PYRETHROIDS

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AND SOIL ALGAE

TABLE 1 Two APPLICATIONS

ALGAL POPULATIONS INSOILASINFLUENCEDBYSINGLEAND ~FCYPERMETHRINORFENVALERATE MPN(X103g-‘soil)of&ae” Pesticide treatment (kg ha-‘) Untreated Cypermethrin 0.5 0.75 1.0 :2 5:o Fenvalerate 0.5 0.75 1.0 1.5 2.5 5.0

Single application 156

Two applications 25

15’

25

15.9 (8.7, 29.2)d

15.9 (8.7,29.2)

18.5 (10.1,33.9)

13.7 (7.4,25.1)

15.9 (8.7,29.2) 15.9 (8.7,29.2) 21.6(11.7,39.6) 11.7 (6.4,21.6) 11.7 (6.4,21.6) 11.7 (6.4,21.6)

13.7 (7.4,25.1) 13.7 (7.4,25.1) 11.7 (6.4,21.6) 13.7 (7.4,25.1) 11.7 (6.4,21.6) 8.7 (4.7, 16.0)

25.3 (13.8,46.4) 21.6(11.7,39.6) 15.9 (8.7,29.2) 15.9 (8.7,29.2) 10.2 (5.5, 18.6) 6.4(<4.1, 11.7)

13.7 15.9 15.9 21.6 25.3 13.7

l&5(10.1,33.9) 21.6(11.7,39.6) 18.5 (10.1,33.9) 18.5 (10.1, 33.9) 15.9 (8.7,29.2) 5.4 (<4.1, 10.0)

15.9 (8.7,29.2) 15.9 (8.7,29.2) 13.7 (7.4,25.1) 10.2 (5.5, 18.6) 10.2 (5.5, 18.6) 10.2 (5.5, 18.6)

15.9 (8.7,29.2) 10.2 (5.5, 18.6) 18.5 (10.1,33.9) 10.2 (5.5, 18.6) 10.2 (5.5, 18.6) 5.4 (<4.1) 10.0)

(7.4,25.1) (8.7,29.2) (8.7,29.2) (11.7, 39.6) (13.8,46.4) (7.4,25.1)

25.3 (13.8,46.4) 90.2 (49.1, 165.6) 153.7 (83.7,282.0) >153.7’(>83.7, >282.0) >153.7 (>83.7, >282.0) > 153.7 (>83.7, >282.0)

’ O-Day(initial) population was 15.9X 10” g-’ soil. b Sampling time (in days)after singleapplication. ‘Sampling time (in days)after secondapplication. “Values in parenthesesrepresent lower and higher fiducial limits, respectively,of each MPN at the 95% confidence level. aNot feasibleto calculatethe exactMPN value as29 of the total 30 culture tubes were scoredpositive for algae.

enhanced the algae greatly by 25 days despite a reduction in the population size under the impact of these concentrations at 15 days. In all of these concentrations, the positive (29 of a total 30) MPN culture tubes contained filamentous blue-greens predominantly. However, attempts were not made to determine the cause for this rapid buildup of the algal flora. Most recently, Caplan et al. (1984) observed no adverse effects on heterotrophic microflora in a marsh sediment (pH 7.8) after 7 days of fenvalerate application at 0.2- and 1.O-ppm levels even though the half-life of this insecticide was less than 9 days. Fenvalerate was also reported to yield three metabolites, 4-OH-fenvalerate (a-cyano-3-(4’-hydroxyphenyl)-benzyl-2-(4-chlorophenyl)i~valerate), CONH*-fenvalerate (a-carbamoyl-3-phenoxybenzyl-2-(4-chlorophenyl)isovalerate), and Cl-vacid or OH-Cl-vacid (2-(4-chlorophenyl) isovaleric acid, seemingly via microbial metabolism and/or hydrolysis in sediments (Caplan et al., 1984) or in soils (Ohkawa et al., 1978). Perhaps these metabolites, formed and accumulated in large quantities in this soil as a consequence of two repeated additions at higher rates, might have either stimulated the germination and growth of algae or indirectly enhanced the growth of algal populations by directly controlling their predators during incubation of the soil samples. A spray schedule involving two applications of a synthetic pyrethroid (cypermethrin or fenvalerate) alternated with a spray of any conventional organophosphate (mainly monocrotophos or quinalphos) between 95 and 135 days was proved to be highly effective in controlling most of the important pests of cotton (Anonymous,

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TABLE 2 EFFECTOF MON~CROTOPHOS

(M) OR QUINALPHOS (Q) APPLICATION BETWEEN Two APPLICATIONS OF CYPERMETHRIN (C) 0~ FENVALERATE (F) ON MPN (x 10’ g-l SOIL) OF ALGAE Sampling

time (in days) after last application

Pesticide treatment (kg ha-‘) Untreated

C-M-C” 1.0 5.0 C-Q-C 1.0 5.0 F-M-F 1.0 5.0 F-Q-F 1.0 5.0

15 21.6 (11.7,39.6)

21.6 (11.7,39.6) 11.7 (6.4,21.6)

25 11.7(6.4,21.6) 8.7 (4.7, 16.0) 7.5 (4.1, 13.7)

18.5 (10.1,34.0) <4.2”(<4.1, <7.0)

11.7(6.4,21.6) 4.6 (<4.1,8.4)

21.6 (11.7,39.6) 11.7 (6.4,21.6)

18.5(10.1,34.0) 4.6 (<4.1,8.4)

21.6 (11.7,39.6) 8.7 (4.7, 16.0)

11.7(6.4,21.6) 6.4(<4.1, 11.7)

a Fifteen days after an initial application (at 1.Oand 5.0 kg ha-‘) of pyrethroid, organophosphate was added at the corresponding levels. Pyrethroid was again added, at the same concentrations, 10 days after organophosphate application. * Not feasible to calculate the exact MPN value since only two of the total 30 culture tubes were scored positive for algae.

1984). This observation prompted us to determine whether there exists any influence of such a schedule on algal populations in soil. Soil treatment of monocrotophos or quinalphos between two applications of a pyrethroid, all at the 1.O kg ha-’ level, was found to have no influence on algae (Table 2). However, an application of quinalphos, at the 5.0 kg ha-’ level, when alternated with two additions of cypermethrin at the same concentration, showed a significant toxic effect at the end of 15 days after the last application. This inhibitory effect is parallel to the reported toxicity of two repeated applications of quinalphos toward algae in the present soil (Megharaj et al., 1986). Also, with the addition of monocrotophos or quinalphos, at 5.0 kg ha-’ and between two applications of fenvalerate, the populations of algae were more affected. This is in contrast to the significant enhancement in the algal flora observed after two repeated additions of this pyrethroid alone even at higher concentrations (Table 1). In general, the filamentous algae, viz., Anabaena variabilis, Lyngbya gracilis, Nostot punctiforme, N. muscorum, N. linckia, Oscillatoria sp., Phormidium tenue, and P. foveolarum, and unicellular forms such as Chlorella vulgaris, Gloeocystis gigas, and Scenedesmus bijugatus, were consistently encountered in all soil samples treated with the pyrethroids. This indicates that the application of pyrethroids effected a change in only the population density of algae and not in their frequency of occurrence. CONCLUSION The results be endangered

of this investigation by the application

suggest that the natural soil algal flora would not of cypermethrin or fenvalerate even at concentra-

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tions in considerable excess to field rates, either repeatedly or alternated with organophosphorus insecticides. REFERENCES ANONYMOUS ( 1984). Recommendations for Cultivation of Cotton in Krishna-Godavari Zone during Kharjf Season 1984-85. Andhra Pradesh Agricultural University, Rajendranagar, Hyderabad. BREESE, M. H., AND HIGHWOOD, D. P. (1977). Cypermethrin, a New Synthetic Pyrethroid Insecticide, pp. 64 l-648. Shel. Research, Sitting Boume, Kent. CAPLAN, J. A., ISENSEE,A. R., AND NELSON, J. 0. (1984). Fate and effect of (I%) fenvalemte in a tidal marsh sediment ecosystem model. J. Agric. Food Chem. 32,166-17 1. FISHER, R. A., AND YATES, F. (1963). Statistical Tablesfor Biological, Agricultural andMedical Research. Oliver & Boyd, Edinburgh/London. HARRIS, C. R., AND TURNBULL, S. A. (1978). Laboratory studies on the contact toxicity and activity in soil of four pyrcthroid insecticides. Canad. Entomol. 110,285-288. JACKSON, M. L. (1958). Soil Chemical Analysis. Prentice-Hall, London. MEGHARAJ, M., VENKATESWARLU, K., AND RAO, A. S. (1986). Effect of monocrotophos and quinalphos on soil algae. Environ. Pollut. A40, 121-126. MORTON, N. (1979). Synthetic pyrethroids on cotton, a spray application strategy. Outlook Agric. 10,7 l77.

MURALIKRISHNA, P. V. G., AND VENKATESWARLU, K. (1984). Effect of insecticides on soil algal population. Bull. Environ. Contam. Toxicol. 33,24 1-245. OHKAWA, H., NAMBU, K., INUI, H., AND MIYAMOTO, J. (1978). Metabolic fate of fenvalerate (sumicidin) in soil and by soil microorganisms. .I. Pestic. Sci. 3, 129- 14 1. ROBERTS, T. R., AND STANDEN, M. E. (1977). Degradation of the pyrethroids cypermethrin NRDC 149 (+)-a-cyano-3-phenoxybenzyl(+)-cis, trans-3-(2,2dichIorovinyl)-2,2dimethyl cyclopropane carboxylate and the respective cis (NRDC 160) and trans (NRJX 159) isomers in soils. Pestic. Sci. 8,305-3 19. SATAPATHY, M. K., AND ANJANEWLU, A. (1984). Use of cypermethrin, a synthetic pyrethroid, in the control of rice tungro virus disease and its vector. Trop. Pest Manage. 30,170- 178. WALKLEY, A., AND BLACK, C. A. (1934). An examination of Degtgamff method for determining soil organic matter and a proposed modification ofchromic acid titration method. Soil Sci. 37,29-38.