Environmental Pollution 59 (1989) 253-264

Loss of HCH from Surface Soil Layers under Sub- tropical Conditions

C. P. Kaushik

Department of Bio-Sciences, Maharshi Dayanand University, Rohtak 124001, Haryana, India

(Received 1 November 1988; revised version received 10 February 1989; accepted 20 February 1989)

A B S T R A C T

The loss of r iCH (hexachlorocyclohexane ) at an application rate of 25 kg ha- 1 was studied under field conditions from two surface soil layers, each of 7"5 cm, at two sites in Delhi. The soil at both sites was sandy loam type, with a pH of 8"2, and 0"8 to 1"0% organic matter content. A t site 1, which was kept .fallow andnot watered, the upper 7.5-cm layer of soil initially lost H C H more rapidly than the lower layer. The half-life of the HCH in the upper and lower 7"5-cm layers was 21 and41 days, respectively, and it was 26 days for the total HC H in the combined 15-era soil layer. A t site 2, which contained ornamental plants and was watered regularly, there was not much difference in the loss of H C H between the upper and lower layers. The halj:l(fe of r iCH was 17 and 25 days for the upper and lower 7"5-cm layers, respectively, and it was 20 days for the total 15-cm soil layer, at this site. The loss was greatest initially at both the sites, and was .faster in wet soil than in dry soil.

I N T R O D U C T I O N

Extensive use of H C H in antimalarial and agricultural operat ions has resulted in its widespread presence in the environment (Kaphalia & Seth, 1978; Kaushik et al., 1987; Agarwal et al., 1987). H C H alone accounts for about 50% of the total insecticides used in India during 1985-86 and

253 Environ. Pollut. 026%7491/89/$03"50 © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain

254 C. P. Kaushik

1986-87 (NMEP & PAl, 1988). A large proportion of the pesticides used reaches the soil and may persist there for varying lengths of time. Studies on the loss of insecticides in soil have generally been carried out in temperate countries, where they may remain in soil for years after their use. A different type of behaviour of these insecticides is to be expected in sub-tropical conditions, due to higher temperature, humidity, precipitation and UV- radiations from the sun. The organochlorine insecticides, which can penetrate a few inches into the soil, persist there for a long time (Stewart & Fox, 1971). Since some insecticides are known to cause disturbances in soil flora and fauna, it was thought worthwhile to study, under field conditions, the distribution, loss and half-life of HCH in the surface layers of dry and wet soils.

MATERIALS AND METHODS

Two sites were selected for the study. Site I was kept fallow and was not watered, whilst at site 2 ornamental plants were grown and it was watered regularly. The experiment was conducted from October 1981 to April 1982. Six plots measuring 5 x 1 m, with a buffer zone of 1 x 1 m, were treated with 10% dust of technical HCH (1.3% ~-HCH) at the rate of 25 kg ha - 1, the rate recommended for the control of various insect pests, and the same number of plots were kept as untreated controls. The soil of the treated and the control plots was thoroughly mixed to a depth of 15 cm, with the help of a spade, before and after applying the insecticide. The soil samples were taken with a soil sampler (76 cm x 3 cm) to a depth of 15 cm. From each plot, five cores were taken and their respective 7.5-cm portions were separated, by first removing the lower 7-5-cm portion from the soil sampler, and then mixed thoroughly to give one composite sample. Three such replicates were taken from each soil layer.

The residues of HCH were extracted by stirring the soil with acetone: hexane (59:41, v/v, Dharam Vir, 1976). Acetone was separated from hexane by shaking with distilled water and the residues from this acetone-water layer were recovered by hexane. The hexane extracts were pooled, concentrated and cleaned with an alumina column (Holden & Marsden, 1969). Standardized aluminium oxide of Brockmann activity grade I-II was kept at 130°C overnight and then partially deactivated with 5% distilled water. It was kept at room temperature for equilibration before use for packing the column. Qualitative and quantitative estimations were performed on a Packard series 7400 gas chromatograph, equipped with an electron capture detector. Instrument parameters and operating conditions were:

Loss of HCH from surface soil layers 255

Column: 180cm glass, 2mm ID packed with 1.5% OV--17/1.95% QF--1 coated on Gas chrom Q, 100 to 120 mesh.

Temperature: column: 190°C detector: 210°C injector: 210°C

Carrier gas: Nitrogen with a flow rate of 75 ml rain- 1

The identifications were further confirmed with another glc column packed with 5% DEGS coated on Gas chrom Q, 100 to 120 mesh, thin layer chromatography (TLC) and chemical dehydrochlorination followed by gas chromatography (Kaushik et al., 1987).

RESULTS

The samples were analysed for the isomers of HCH.* The percentage recoveries from 10g soil sample fortified with 100ng each of the HCH isomers were 107, 98 and 96%, respectively, for ~, 7 and// /6-HCH. The data have not been corrected for recovery rates.

The soil at both the sites was of sandy loam type and had a pH of 8"2. The organic carbon content was 0.8% at site 1, and 1.0% at site 2. The environmental conditions, such as air and soil temperatures, rainfall and relative humidity, were recorded during the experiment and are given in Fig. 1.

Site 1

As a result of the soil treatment, the upper 7.5-cm layer received 92"5% resulting in a concentration of 0"5/~g g-1, whereas the lower 7"5-cm layer received only 7-5% of total HCH applied, resulting in 0.048/~g g- 1 (Figs 2 and 3). The loss of HCH from the soil was rapid, initially. Sixty days after application the upper layer had lost 92-7%, and the lower layer had lost 7.5%, of the total HCH applied to the respective layers, resulting in a total loss of 86.4% from both layers (Fig. 4). The loss of r iCH increased to 96.8% from the upper layer and 10% from the lower layer after 90 days, resulting in a total loss of 90"3%. Subsequently, by 150 days 99.2% of HCH had been lost from the upper layer, while the lower layer had lost 87.5%, resulting in a total loss of 98.3%. After 180 days the upper layer had lost 99%, while the lower layer had lost 92"5% during the same period, thereby increasing the

* On the basis of the glc analysis technical HCH used in the experiments consisted of 82% ~, 13% 7 and 5% [~/6-HCH.

256 C. P. Kaushik

Fig. 1.

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Loss of HCH from surface soil layers 257

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loss from both the layers to 98.5%. The half-life of total HCH at this site was 21 days for the upper 7.5-cm soil layer, 41 days for the lower soil layer and 26 days in the total 15-cm soil layer (Table 1).

Among the various isomers present in technical HCH, the ~ and 7-isomers were lost at a very fast rate, whereas the concentration of fi/f-isomers remained at a very low and relatively constant level. Within 60 days of treatment 93.1% of the s-isomer had been lost from the upper layer of soil, and this loss had increased to 99"2% in 180 days. During the same period the loss of 7-HCH was 90.9 and 99%, respectively (Fig. 2).

In general the loss of HCH isomers from the lower layer was comparatively slow. During the first 60 days, only 23% of },-HCH was found to have been lost from this layer. Almost all of the 7-HCH was lost from the soil by 180 days, while ct-HCH apparently did not show any appreciable loss during the first 60 days. However, by 180 days 92"6% of ~-HCH had been lost (Fig. 3).

258 C. P. Kaushik

Fig. 3.

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TABLE 1 Half-lives (Days), Rate Cons tan t s K (day-1) and r-values

Upper 7"5 cm Lower 7"5 cm Total 15 cm

Site 1 Half-lives 21

Rate cons tan ts - 0 ' 0 3 3 r-values 0-868

Site 2 Half-lives 16.9 Rate cons tan ts - 0 ' 0 4 1 r-values 0-896

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260 C. P. Kaushik

Site 2

As a result of the treatment, the upper layer received 71.7% and the lower layer 28.3 % of the total HCH applied, resulting in a concentration of 0.502 and 0.204 #g g- 1, respectively (Figs 5 and 6). Sixty days after the application, the upper and the lower layers lost 93.9 and 93.1%, respectively, of the total HCH present in the respective layers. The total loss from both the layers was 93.7% of the total HCH applied to the 15-cm of soil (Fig. 7). The loss increased to 99.1% in the upper layer and to 89.1% in the lower layer after 90 days. The total loss from both the layers thus increased to 96.3%. After 120 days the upper layer had lost 97-7% and the lower layer 94.8%, so that the total loss from both the layers was 96-9% (Fig. 7). The half-life of total HCH at this site was 17 days for the upper 7.5-cm soil layer and 25 days for the lower soil layer, and it was 20 days for the total 15-cm soil layer (Table 1).

Among the various isomers, the ~- and y-isomers were lost at a fast rate. The upper layer lost 92.9% of ~-HCH after 60 days. The loss increased to 96"9% after 90 days and 97"2% after 120 days. About 98.9% of y-isomer was lost within 90 days (Fig. 5). Unlike at site 1, the loss of the various isomers

Fig. 6.

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Concentration of HCH in lower 7.5 cm (wet) soil treated with 10% technical HCH at the rate of 25 kg ha- 1.

Loss of HCH from surface soil layers 261

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from the lower layer of soil at site 2 was similar to that from the upper layer. Almost 95% of T-HCH was lost by 60 days and 82"4% of T-HCH was lost during the same period. The loss of 7-HCH further increased to 97.1% by 120 days (Fig. 6). Since the quantities of fill-isomers detected were very low the exact percentage of their loss could not be assessed.

DISCUSSION

When soil was treated with HCH it was found that, at site 1, the upper layer contained most of the HCH, while this was less marked at site 2. This

262 C. P. Kaushik

variation may be attributed to the watering of site 2, which probably allowed more HCH to move downwards. Site 1 was not watered during the course of the experiment. The higher percentage of HCH in the upper layer at site 1 may also have been due to the fact that dry soils adsorb pesticides more strongly (Taylor, 1978). At site 2, the moisture deactivated the soil (Bowman et al., 1965) prior to addition of riCH. Tl~is allowed some of it to penetrate to the lower soil (Moreale & Van Bladel, 1978). No attempt was made to estimate the HCH residues in the plants growing in the plots, or bound to the soil, since HCH is feebly systemic (Harvey, 1983) and does not bind to the soil to a large extent (Stewart & Fox, 1971). At site 1, total loss of r iCH was 86% within 60 days, whilst in the same time, site 2 registered a loss of about 93%. The difference of loss of HCH at the two sites was found to be statistically significant ( t= 4-26, p < 0-05, d f = 4). This loss was perhaps mainly due to volatilization, which is known to be highest immediately after application, before the pesticide is fully sorbed onto or into the treated surface (Seiber et al., 1979).

The total loss of HCH from site 2 was greater throughout the period of investigation. This appears to be due to the fact that loss of pesticide from moist soil is faster than from dry soil (Lichtenstein et al., 1977). Piasecki et al. (1971) also reported that an increase in moisture from 40 to 95% speeded up the disappearance of DDT and HCH in all the samples with different physico-chemical properties. The present data indicate that the loss of HCH from the upper layer was greater than that from the lower one at site 1, while at site 2 this difference was less marked. This may be due to the 'wick-up' action of water in moist soil, which helps to bring more of the pesticide to the surface (Lichtenstein et al., 1960). Rapid degradation and dissipation of HCH may also be due to the fairly high alkalinity of the soil at both the sites, which may cause alkaline hydrolysis.

Among the HCH isomers, the a-isomer was lost at the fastest rate, followed by the 7-isomer. Quantities of fl- and 6-isomers were very low in this formulation, and hence it was difficult to calculate their rates of dissipation. However, their relatively constant levels show them to be quite persistent in soils (Figs 2-7). The volatility of these isomers is related to their vapour pressures (MacRae et al., 1967).

The loss of r iCH observed in the present study is far faster than the results obtained in temperate conditions. Edwards (1973) reported the time for disappearance of 95% oflindane applied at about 1 lb acre 1 to be 6-5 years, with the half-life of 1.2 years. This is in contrast to half-life of 26 and 20 days in dry and wet soils, respectively, for HCH applied at the rate of 25 kg ha- 1, in the present experiment. A still faster rate of loss can be expected during the summer months.

Loss of HCH Jrom surface soil layers 263

A C K N O W L E D G E M ENTS

The author wishes to thank Prof. M. K. K. Pillai and Prof. H. C. Agarwal of the Depar tment of Zoology, University of Delhi, Delhi, for encouragement, and for providing facilities. The financial assistance from the University Grants Commission, New Delhi, is also thankfully acknowledged.

R E F E R E N C E S

Agarwal, H. C., Kaushik, C. P. & Pillai, M. K. K. (1987). Organochlorine insecticide residues in the rain water in Delhi, India. Water, Air & Soil Pollut., 32, 293 302.

Bowman, M. C., Schechter, M. S. & Carter, R. L. (1965). Behavior of chlorinated insecticides in a broad spectrum of soil types. J. Agric. Food Chem., 13, 360 5.

Dharam Vir. (1976). Studies on Levels of DDT Residues in Soil and Human Blood in Delhi and its Metabolism in Certain Animals. PhD Thesis, Univ. of Delhi.

Edwards, C. A. (1973). Persistent Pesticides in the Environment, Chemical Rubber Co. Press, Cleveland (2nd edn).

Harvey, J., Jr (1983). A simple method of evaluating soil breakdown of 14C- pesticides under field conditions. Residue Rev., 85, 149-58.

Holden, A. V. & Marsden, K. J. (1969). Single stage clean-up of animal tissue extracts for organochlorine residue analysis. J. Chromatog., 44, 481 92.

Kaphalia, B. S. & Seth, T. D. (1978). Isomers and metabolites of DDT and BHC in blood plasma, adipose tissue and cerebro-spinal fluid (CFS) of persons of Lucknow. Indian J. Biochem., Biophys., 15, 79.

Kaushik, C. P., Pillai, M. K. K., Raman, A. & Agarwal, H. C. (1987). Organochloride insecticide residues in air in Delhi, India Water, Air & Soil Pollut., 32, 63-76.

Lichtenstein, E. P., DePew, L. J., Eshbaugh, E. L. & Sleesman, J. P. (1960). Persistence of DDT, aldrin and lindane in some midwestern soils. J. Econ. Entomol., 53, 136~,2.

Lichtenstein, E. P., Katan, J. & Anderegg, B. N. (1977). Binding of'persistent' and 'non-persistent' 14C-labelled insecticides in an agricultural soil. J. Agric. Food Chem., 25, 43-7.

MacRae, I. C., Raghu, K. & Castro, T. F. (1967). Persistence and biodegradation of four common isomers of benzenehexachloride in submerged soils. J. Agric. Food Chem., 15, 911-14.

Moreale, A. & Van Bladel, R. (1978). Adsorption and leaching of lindane in soils. Parasitica, 34, 233 55.

National Malaria Eradication Programme (NMEP), New Delhi & Pesticide Association of India (PAl), New Delhi (1988).

Piasecki, J., Wybieralski, J. & Wybieralska, A. (1971). Effect of moisture on speed of disappearance of DDT and BHC from soils with different physical and chemical characteristics. Zesz. Nauk. Wyzsz. Szk. Roln. Szezecinie., 8, 271 -82.

Seiber, J. N., Madden S. C., McChesney, M. M. & Winterlin, W. L. (1979). Toxaphene dissipation from treated cotton field environments: Component

264 C. P. Kaushik

residual behaviour on leaves and air, soil and sediments determined by capillary gas chromatography. J. Agric. Food Chem., 27, 284-90.

Stewart, D. K. R. & Fox, C. J. S. (1971). Persistence of organochlorine insecticides and their metabolites in Nova Scotian Soils. J. Econ. Entomok, 64, 367-71.

Taylor, A. W. (1978). Post-application volatilization of pesticides under field conditions. J. Air Pollut. Control Assoc., 28, 922-7.