Ecotoxicology and Environmental Safety 42, 203—206 (1999)

Environmental Research, Section B

Article ID eesa.1998.1743, available online at http://www.idealibrary.com on

Effect of Natural Dissolved Humic Material on Bioavailability and AcuteToxicity of Fenpropathrin to the Grass Carp, Ctenopharyngodon idellus

W. Z. Wu,*,-,1 Y. Xu,* K.-W. Schramm,‡ and A. Kettrup-,‡*State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Wuhan 430072, Peoples Republic of China;

‡Institute of Ecological Chemistry, GSF-National Research Center for Environment and Health, Ingolstaedter Landstrasse 1, D-85764 Neuherberg,Germany; and -Lehrstuhl fu( r O$ kologische Chemie und Umweltanalytik, Techn. Universita( t Mu( nchen, Munich, Germany

Received May 6, 1997

The effects of aquatic humic acids on the bioconcentration andacute toxicity of fenpropathrin were evaluated using grass carp,Ctenopharyngodon idellus, in laboratory freshwater systems.The results demonstrated that both bioavailability and acutetoxicity decreased in the presence of aquatic humic acid 5 and10 mg/ liter. In addition, the extent of influence increased withincreasing concentration of aquatic humic acid. ( 1999 Academic Press

Key Words: humic acids; fenpropathrin; bioavailability;toxicity.

INTRODUCTION

In recent years, fenpropathrin, a new synthetic analogueof pyrethroid insecticides, was imported in large amountsand widely used in China, especially in the south of thecountry, to control insect pests in staple crops such ascereals, potatoes, tobacco, cotton, and fruit. The commercialname of the pesticide is Meothrin, and the chemical name is2,2,3,3-tetramethylcyclopropanecarboxylic acid cyano(3-phenoxyphenyl) methyl ester. The contamination of surfacewaters in agricultural areas by synthetic pyrethroidsthrough overspray, drift, or runoff is of concern, becausethese compounds have been found to be extremely toxic toaquatic organisms (Smith and Stratton, 1986).

Dissolved humic materials (DHM) generally occur innatural waters and represent a major component of the totaldissolved organic carbon (Chiou et al., 1986). DHM areconsidered to play a very important role in the fate andtransfer of organic pollutants in aquatic environments.Because DHM can change the physicochemical state orspecificity of these pollutants in aquatic systems by bindingor associating with them, including alterations of watersolubility, hydrolysis kinetics (Hasseff and Milicic, 1985;Chiou et al., 1986; James et al., 1990), bioavailability, and

1To whom correspondence should be addressed in Germany.

203

toxicity (Servos et al., 1989; Kristin, 1991; Lee and Freitag,1993). However, most of these authors selected only Aldrichhumic acid as the source of DHM for their studies. Thiscommercially available form of DHM is considered not torepresent natural aquatic DHM. To better understand andpredict the potential hazard of fenpropathrin and the inter-action between it and DHM in aquatic environments, thepresent study was carried out to evaluate the effect of DHMon the bioavailability and acute toxicity of fenpropathrin toCtenopharyngodon idellus.

MATERIALS AND METHODS

1. Chemicals

Pure fenpropathrin was prepared in the laboratory (pu-rity'98%) by the following procedure: Commercial gradeMeothrin (purity"20%) was purified by silica columnchromatography and then recrystallized in benzene. All thereagents including petroleum ester, acetone, anhydrous so-dium sulfate, and acetic acetate were analytically pure andverified by GC. Acetone was used as a carrier solvent fordissolving the chemicals.

Dissolved humic acid was obtained from Ecological andEnvironmental Research Center, Beijing, China; it had beenisolated from the Lianjiang River in South China. Charac-teristic parameters of DHM used were C 62.66%, H 5.07%,N 1.21%, and ash 0.80%. The results of functional groupanalysis were total acidic, 6.57 meq/g; carboxylic, 3.7 meq/g;phenolic, 2.87 meq/g; and quinonic, 1.8 meq/g. The DHMstock solution was prepared by dissolving 500 mg DHM in50 ml of Milli-Q deionized water, adding 3—4 drops of 10%NaOH solution, and finally diluting in 1 liter Milli-Q de-ionized water.

2. Experimental Animals

Ctenopharyngodon idellus was obtained from the Instituteof Hydrobiology, Wuhan, China, and kept in large tanks

0147-6513/99 $30.00Copyright ( 1999 by Academic Press

All rights of reproduction in any form reserved.

FIG. 1. Effect of DHM on accumulation of fenpropathrin in fish.

204 WU ET AL.

under running water of 1 week prior to the tests. Fish werefed daily before they were introduced into the exposureaquarium. The average body weight of fish is about 10 g(wet weight).

3. Bioconcentration Experiment

All exposures of fish to fenpropathrin were conducted ina static water system. Water was filtered in an activatedcarbon column. The routine parameters of water weremonitored: pH 7.8, temperature 20($) 0.5°C, NH

40.4 mg/

liter, Cl~ 7.5 mg/liter. The test concentration of fenpropath-rin was 1 lg/liter, to which the DHM stock solution wasadded to give the desired DHM concentration (0, 1, or10 mg/liter) and then vigorously stirred.

For accumulation experiments, 20 fish each were placedinto 15-liter aquaria. The animals were not fed during theexperiment. The aquaria were wrapped with foil to protectfrom light exposure. Storage in darkness was necessarybecause photodegradation of fenpropathrin has been re-ported. During the test, two fish were removed at0, 2, 4, 8, 10, and 12 h, rinsed, blotted dry, and weighed.After being weighed, they were analyzed as soon as possible.The concentrations of fenpropathrin in water were mea-sured at the same time the fish were sampled.

4. Toxicity Test

In consideration of the biodegradation and high toxicityto aquatic organisms, the mortality (%) caused by fenpro-pathrin after 8 h was used as the acute toxicity endpoint.The experiment was conducted in three test groups. Theconcentrations of DHM for these three groups were 0, 1,and 10 mg/liter. In each group, nine aquaria were used, andthe anticipated concentrations of fenpropathrin were 0, 1.8,2.1, 2.4, 2.8, 3.2, 4.2, 5.6, and 6.1 lg/liter. Each concentrationwas replicated three times and each aquarium contained 20small fish (less than 2 months of age) in 1 liter water. Theweight of test fish ranged from 1.0 to 1.2 g. Finally, thepercentage mortality was calculated.

5. Residual Analysis

Water samples were extracted with petroleum ester andthe organic phase was concentrated and analyzed by GC.Fish muscle was minced, homogenized, and mixed withanhydrous sodium sulfate. The mixture was then extractedwith acetone three times. The combined acetone phase wasintroduced by 2% (w/v) Na

2SO

4solution following petro-

leum ester. Anhydrous sodium sulfate was used to removethe trace amount of water in the petroleum ester extract,which was concentrated to about 1 ml afterward.

The extracts were cleaned by passage through a Na2SO

4—

Florisil—Al2O

3column. The petroleum ester: acetic acetate

(20:1, v/v) was allowed to pass through the column. Finally,the collected portion was concentrated and the residue wasdissolved in 1 ml petroleum ester. The total recoveries of themethod averaged 89.57($) 5.37%.

Fenpropathrin residues were determined with a HP5890Acapillary gas chromatograph, equipped with electron cap-ture detector (ECD). A fused silica capillary column (30 mlong]0.32 mm i.d.) with bound phase OV-101 was oper-ated at 250°C, with N

2as carrier gas. The detection and

injection temperature was 280°C.

RESULTS

1. Effect of DHM on Uptake of Fenpropathrin in Fish

Figure 1 presents the results of the accumulation of fen-propathrin by C. idellus from water with and without DHM.After 8 h, the concentration of fenpropathrin in fish reachedthe maximum of 40 ng/g. But in the presence of 1 and10 mg/liter DHM, the maximum concentration and timeare 29.5 ng/g, 6 h, and 20 ng/g, 4 h, respectively. Fenpro-pathrin concentrations in fish were reduced in the presenceof 1 and 10 mg/liter DHM in water, indicating that DHMcan bind with fenpropathrin to form a DHM—fenpropathrincomplex (Table 1). The highest concentration of DHM(10 mg/liter, compared with 0 and 1 mg/liter) caused lessbioavailability, as evidenced by the lower accumulation offenpropathrin by C. idellus from water. It is clear thatbioaccumulations is reduced by an increase in DHM con-centration.

Figure 2 presents the decline in fenpropathrin in water. Itwas observed that the higher the concentration of DHM inwater, the smaller the concentration of fenpropathrin detec-ted, probably because the bound fenpropathrin in watercould not be extracted by the organic solvent.

TABLE 1Free and Bound Concentrations of Fenpropathrin in Water in the Presence of Aquatic Humic Acids at Different Concentrations

0 mg/liter DHM 1 mg/liter DHM 10 mg/liter DHM

Time (h) Total free Fenpro Fenpro in fish Free Fenpro Fenpro in fish Binding Fenpro Free Fenpro Fenpro in fish Binding Fenpro

8 500a 38 300 27 200 140 16 3606 550 35 400 29.5 150 210 18 3402 670 18 620 16 40 500 13 170

a All values are in mg/liter.

HUMIC ACID EFFECTS ON FENPROPATHRIN IN GRASS CARP 205

2. Effects of DHM on Acute Toxicity of Fenpropathrinto Ctenopharyngodon idellus

Figure 3 presents the LC50

values LC50

of fenpropathrinto C. idellus in the presence of 0, 1, and 10 mg/liter DHM:2.51, 3.72, and 4.68 lg/liter, respectively. The LC

50values

represent the concentrations at which 50% of the fish diedin 8 h. Mortality C. idellus decreased in the presence of 1 and10 mg/liter DHM. The results indicated that fenpropathrinLC

50values were increased compared with the control

without DHM. The acute toxicity of fenpropathrin wasapproximately twofold less at 10 mg/liter DHM than in thecontrol. Furthermore, the acute toxicity (LC

50) of fen-

propathrin was found to decrease as DHM concentrationincreased.

DISCUSSION

The results in Table 1 and Fig. 1 are quite similar to otherreports for fish and aquatic invertebrates exposed to hydro-phobic contaminants (Servos et al., 1989). Muir et al. (1989)and Kristin (1991) found that accumulations of other syn-

FIG. 2. Effect of DHM on the decline of fenpropathrin in water.

thetic pyrethroids, e.g., deltamethrin, fenvalerate, and cyalo-thrin, were reduced by 20 to 80% in Daphnia magna in thepresence of Aldrich HA and natural aquatic humus. Otherstudies (e.g., Saint-Fort and Visser, 1988) have demon-strated that hydrophobic contaminants can form stablecomplexes with dissolved colloidal materials, resulting inenhancement of the water solubility of the contaminant. Assuggested by Landrum et al. (1985), the contaminant doesnot have sufficient time to diffuse out of the complex andmove by passive diffusion across respiratory membranes orintegument, and is therefore unavailable for uptake by bi-ota, because the bonds in the DHM—pesticide complex areeither too large or too polar to penetrate across biologicalmembranes. The observed reduction in bioavailability iscaused by the increase in DHM concentration becauseC. idellus is able to accumulate only the truly free fenpro-pathrin in water.

Since the water solubility of fenpropathrin is reported as0.34 lg/g, and the octanol/water partition coefficient as1000, fenpropathrin is apparently a typical hydrophobiccontaminant. Some investigations (McCarthy and Jimenez,1985; Landrum et al., 1984) have demonstrated that affinityof an organic compound to DHM is inversely related to thewater solubility of the given organic compound. In other

FIG. 3. Effect of DHM on acute toxicity of fenpropathrin in fish.

206 WU ET AL.

words, increasing DHM concentration in water can en-hance the water solubility of fenpropathrin, thereby alteringthe partitioning between water and organism. In the presentstudy, the enhancement of water solubility was demon-strated by the increase in fenpropathrin bound to DHM inwater, and the bioconcentration factor (BCF) of C. idelluswas reduced by the same level. This indicated that thereduction in bioavailability caused by DHM depended onthe extent of binding between fenpropathrin and DHM. Asa result, the bioavailability of fenpropathrin can be dramati-cally reduced in aquatic environments containing relativelyhigh concentrations of DHM.

Fenpropathrin has been reported to be a highly effectiveand low-residue pesticide for controlling insect pests, butit is now known to be extremely toxic to aquatic organisms.Therefore, care should be exercised in the application ofthis compound in aquatic systems. The results in Fig. 3indicate that DHM can be a detoxicant of fenpropathrin toC. idellus. The decrease in bioavailability of fenpropathrinto aquatic biota should result from a reduction in theorganisms, exposure to a potential dose. It is possible thatthe presence of DHM in water may affect the state ofdiffusion of free dissolved contaminants through biologicalmembranes. Whatever the mechanism, the result of thisstudy demonstrate that the interaction between fenpropath-rin and natural DHM can alter the bioavailability andtoxicity of the pesticide. In addition, the extent of alterationis probably dependent on the source and compositionof DHM.

CONCLUSIONS

1. The results of this study demonstrated that the interac-tion between fenpropathrin and natural DHM can alter thebioavailability and toxicity of the pesticide. Both the bio-availability and acute toxicity were decreased in the pres-ence of aquatic humic acid 5 and 10 mg/liter.

2. The extent of the influence was increased with increas-ing concentration of aquatic humic acid.

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