**4. Results and discussion**

The highest concentration of HCH was found in the sampling month of October (213 ng/g) (Manko estuary) and Dieldrin (98 ng/g) (Okukubi estuary) followed by the month of Novem‐ ber (HCH-199 ng/g) (Manko estuary) and (Dieldrin-90 ng/g) (Okukubi estuary). The status of HCH and dieldrin in sediments in this study was compared with those in other rivers. The levels of OCPs in this study are lower than that of Er-jen river, Taiwan (80-8200 ng/g (dw)) (Zhang et al.*,* 2002). River Mataniko, Solomon Island (140 ng/g (dw)) (Iwata et al.*,* 1995) but higher in some rivers in Japan (2.5-12 ng/g (dw)) (Sakar et al.*,* 1997).The basic physico-chemical parameters of sediments such as TOC were also measured. The TOC contents ranged from nd-3.96% (Table 3 and Table 4). Figure 4-Figure 5 shows a positive correlation with the concentration of HCH especially in the Manko estuary. No correlation was shown between HCH and TOC from the Okukubi estuary. It is clear that sediments from the Okukubi estuary were composed of fine particles. This observation is consistent with other studies which demonstrated that fine particles can retain large amounts of organic compound and pose a high pollution potency (Hong et al.*,* 1995). Since HCH and dieldrin exhibit carcinogenic activities, the contamination levels detected may pose a high ecotoxicity for aquatic and marine organisms.

**Sample Temperature (ºC) pH Total Organic Carbon (%)**

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O-26s 25.4 8.06 3.96 O-27s 25.9 8.00 2.82 O-28s 26.0 7.99 2.11 O-29s 26.2 7.99 1.76 O-30s 26.5 7.78 0.54 O-31s 26.9 7.56 nd O-32s 27.0 7.69 nd O-33s 27.2 7.69 nd O-34s 27.0 7.72 nd O-35s 27.1 7.71 nd O-36s 27.1 7.60 nd O-37s 26.8 7.64 nd O-38s 26.9 7.64 nd O-39s 26.9 7.58 nd O-40s 26.9 7.54 nd

nd: not detected

**Table 4.** Summary of Environmental Parameters – Okukubi Estuary

**Figure 4.** Correlation of HCH with TOC [Manko estuary]


**Table 3.** Summary of Environmental Parameters – Manko Estuary

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nd: not detected

(Zhang et al.*,* 2002). River Mataniko, Solomon Island (140 ng/g (dw)) (Iwata et al.*,* 1995) but higher in some rivers in Japan (2.5-12 ng/g (dw)) (Sakar et al.*,* 1997).The basic physico-chemical parameters of sediments such as TOC were also measured. The TOC contents ranged from nd-3.96% (Table 3 and Table 4). Figure 4-Figure 5 shows a positive correlation with the concentration of HCH especially in the Manko estuary. No correlation was shown between HCH and TOC from the Okukubi estuary. It is clear that sediments from the Okukubi estuary were composed of fine particles. This observation is consistent with other studies which demonstrated that fine particles can retain large amounts of organic compound and pose a high pollution potency (Hong et al.*,* 1995). Since HCH and dieldrin exhibit carcinogenic activities, the contamination levels detected may pose a high ecotoxicity for aquatic and marine

434 Insecticides - Development of Safer and More Effective Technologies

**Sample Temperature (ºC) pH Total Organic Carbon (%)**

K-26s 26.5 8.01 3.13

K-27s 27.4 7.86 2.74

K-28s 28.4 7.81 1.29

K-29s 27.9 7.43 0.24

K-30s 27.6 7.56 nd

K-31s 27.6 7.66 nd

K-32s 28.9 7.74 nd

K-33s 28.9 7.65 nd

K-34s 28.2 7.55 nd

K-35s 28.2 7.64 nd

K-36s 28.6 7.62 nd

K-37s 28.6 7.58 nd

K-38s 28.9 7.56 nd

K-39s 28.9 7.58 nd

K-40s 28.9 7.56 nd

**Table 3.** Summary of Environmental Parameters – Manko Estuary

organisms.

nd: not detected

**Table 4.** Summary of Environmental Parameters – Okukubi Estuary

**Figure 4.** Correlation of HCH with TOC [Manko estuary]

China (0.14–1.12 ng/g, with a mean value of 0.45 ng/g dw, Hong et al.*,* 1995) and Casco Bay, USA (<0.25– 0.48 ng/g) dw, but lower than the Matanico River and Solomon Islands (140

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It clearly revealed that the HCH and dieldrin pesticides residues in October were higher compared to other sampling months. This means that some organochlorine pesticides could be released from the run-off effluents to waters with much rainfall during the rainy season and typhoon season in Okinawa during the summer. In all sampling months, the highest concen‐ tration of organochlorine pesticides in the Manko estuary was 213 ng/g (dw) in October and for the Okukubi estuary, the highest concentration of organochlorine pesticides was also detected in the month of October, 213 ng/g (dw). The second highest concentration of HCH was detected in the month of November (199 ng/g (dw)) followed by the month of December (99 ng/g (dw)) for the Manko estuaries. The second highest concentration of dieldrin was detected in the month of October (90 ng/g (dw)), followed by 89.5 ng/g (dw) in the month of

Composition difference of HCH in the environment could indicate contamination sources (Wu et al.*,* 1999). Technical HCH has been used as broad spectrum pesticides for agricultural purposes, which has been banned in the 1970's in Japan. Technical-grade HCH consists principally of four isomers, α-HCH, β-HCH, γ-HCH and δ-HCH. The physiochemical properties of these HCH isomers are different. The β-HCH has the lowest water solubility and vapour pressure which is the most stable and relatively resistant to microbial degradation (Strandberg et al.*,* 1998). Also it should be noted that α-HCH can be converted to β-HCH in the environment (Lee et al.*,* 2001). The results showed that a high percentage of HCH isomer was recorded in the sampling months December, January and February. It is possible that HCH may be re-absorbed to surface sediments. There was no strong evidence to prove the recent

usage of HCH in Okinawa; however Manko estuary was contaminated with HCH.

Generally the distribution of organochlorine pesticides were associated with land use practices including agriculture and urbanization and the sediments from estuary have higher contents of organic matter such as TOC and organochlorine pesticides residues. The concentration and compositions of organochlorine pesticides varied significantly with different sampling sites. The HCH in the surface sediments were well correlated with TOC content. The organochlorine pesticides residues (HCH and dieldrin) were detected due to re-absorption in sediments due to previous deposition. The possible sources of these organochlorine pesticides are still unknown but they may come from residential areas, commercial and naval ports and agricul‐

ng/g) (Walker et al., 1999).

November for the Okukubi estuaries.

**5. Conclusion**

ture activities.

**4.3. Composition analyses in sediments**

**4.2. Monthly variations of HCH and dieldrin in sediments**

**Figure 5.** Correlation of Dieldrin with TOC [Okukubi estuary]

#### **4.1. Spatial distribution of HCH and dieldrin in sediments**

The highest concentrations of HCH was found in sample K-26s – 213 ng/g (dw) (Manko estuary) and the highest dieldrin concentration was found in sample O-26s – 98 ng/g (dw) (Okukubi estuary). Most samples in the Okukubi estuary had relatively low levels of HCH compared to Manko estuary, where the sediments mainly composed of sand. It may be due to the similar historical input and deposit indicating important sources of these organochlorine pesticides in these areas. The second highest concentration of HCH in the Manko estuary, 99 ng/g (dw) followed by 90 ng/g (dw). The second highest concentration of dieldrin in the Okukubi estuary was 199 ng/g (dw) followed by 95.5 ng/g (dw). The levels of HCH and dieldrin in this study are higher in those found in the sediments of the Mingjiang River Estuary, China (2.99–16.21 ng/g, with a mean value of 8.62 ng/g dw (Kennicutt et al.*,* 1994). the Wushi Estuary, Taiwan (0.99–14.5 ng/g, with a mean value of 3.78 ng/g dw (Iwata et al.*,* 1995) Xiamen Harbor, China (0.14–1.12 ng/g, with a mean value of 0.45 ng/g dw, Hong et al.*,* 1995) and Casco Bay, USA (<0.25– 0.48 ng/g) dw, but lower than the Matanico River and Solomon Islands (140 ng/g) (Walker et al., 1999).

#### **4.2. Monthly variations of HCH and dieldrin in sediments**

It clearly revealed that the HCH and dieldrin pesticides residues in October were higher compared to other sampling months. This means that some organochlorine pesticides could be released from the run-off effluents to waters with much rainfall during the rainy season and typhoon season in Okinawa during the summer. In all sampling months, the highest concen‐ tration of organochlorine pesticides in the Manko estuary was 213 ng/g (dw) in October and for the Okukubi estuary, the highest concentration of organochlorine pesticides was also detected in the month of October, 213 ng/g (dw). The second highest concentration of HCH was detected in the month of November (199 ng/g (dw)) followed by the month of December (99 ng/g (dw)) for the Manko estuaries. The second highest concentration of dieldrin was detected in the month of October (90 ng/g (dw)), followed by 89.5 ng/g (dw) in the month of November for the Okukubi estuaries.

#### **4.3. Composition analyses in sediments**

Composition difference of HCH in the environment could indicate contamination sources (Wu et al.*,* 1999). Technical HCH has been used as broad spectrum pesticides for agricultural purposes, which has been banned in the 1970's in Japan. Technical-grade HCH consists principally of four isomers, α-HCH, β-HCH, γ-HCH and δ-HCH. The physiochemical properties of these HCH isomers are different. The β-HCH has the lowest water solubility and vapour pressure which is the most stable and relatively resistant to microbial degradation (Strandberg et al.*,* 1998). Also it should be noted that α-HCH can be converted to β-HCH in the environment (Lee et al.*,* 2001). The results showed that a high percentage of HCH isomer was recorded in the sampling months December, January and February. It is possible that HCH may be re-absorbed to surface sediments. There was no strong evidence to prove the recent usage of HCH in Okinawa; however Manko estuary was contaminated with HCH.
