**2. Environmental impact to estuaries**

Organochlorine pesticides are carbon-based chemicals that contain bound chlorine. These compounds are hydrophobic and lipophilic to varying degrees, meaning their solubility in water is very low, whereas their solubility in fats and oils is relatively high (Cheevaporn et al.*,* 2005).They are noted for their persistence and bioaccumulation characteristics. The widespread use of these compounds over the past half century has led to their detection in many hydrologic systems world-wide from agricultural and non-agricultural purposes (Monirith et al.*,* 2003). The presence of HCH and dieldrin pesticides in the environment may be related to both past and present land use in a watershed. It enters the aquatic environment from a variety of sources, including the atmosphere, industrial and municipal effluents and agricultural and urban non-point source run-off. HCH and dieldrin are mostly associated with bottom sediments, which can be ingested by benthic organisms. These organisms are then eaten by fish and birds, which can result in higher concentrations through aquatic and terrestrial food chains. Due to the long residence time of these substances in the environment, it is important to examine the pollution they cause not only the environment but also for the lower invertebrates such as corals. Since the ocean is the receiving basin for terrigenous freshwater run-off and its entrained materials, some fractions of these compounds that are used in upland eventually reach the marine ecosystems.

The Manko and Okukubi estuaries are protected wetlands located in a subtropical climate on Okinawa Island. These estuaries are very famous host for migrating birds from South East Asia and mainland Japan. It also plays a great role of species conservation and it was added to the RAMSAR Convention register of wetlands. However, estrogenic activities were detected in sediment samples from these estuaries (Tashiro et al.*,* 2007). Previous studies showed that the coral reef ecosystems and their adjacent environments in and around the Okinawa Island are contaminated with OCPs, OTCs and PCBs (Tashiro et al.*,* 2003; Imo et al.*,* 2007; Sheikh et al.*,* 2002). However, very little is known about the behaviour of HCH and dieldrin in estuarine sediments of subtropical areas. The main objective of this chapter is provide crucial informa‐ tion on the distribution and behaviour of HCH and dieldrin compounds in protected sub‐ tropical estuaries in the Okinawa Island.

**Estuary Transect Sample Location Activities**

Spatial and Monthly Behaviour of Selective Organochlorine Pesticides in Subtropical Estuarine Ecosystems

K-28s-05

K-31s-05

K-34s-05

K-37s-05

K-40s-05

O-28s-05

O-31s-05

O-34s-05

O-37s-05

O-40s-05

TM2 K-29s-05

TM3 K-32s-05

TM4 K-35s-05

TM5 K-38s-05

TO2 O-29s-05

TO3 O-32s-05

TO4 O-35s-05

TO5 O-38s-05

**Table 1.** Details of sampling areas.

Okukubi TO1 O-26s-05

K-27s-05 Upstream Residential area

http://dx.doi.org/10.5772/54842

431

K-30s-05 Mid –stream Residential area

K-33s-05 Mid-stream Residential area

K-36s-05 River mouth Residential and fishing port

K-39s-05 Naha port Commercial port

O-27s-05 Upstream Agriculture

O-30s-05 Mid-stream Agriculture

O-33s-05 Mid-stream Agriculture

O-36s-05 Mid-stream Fishing area

O-39s-05 River mouth Residential, public area

Manko TM1 K-26s-05
