Pesticide Residues in Fish - Pesticides: Evaluation of Environmental Pollution - page 376

to 28 tg/kg wet weight in silver-banded croaker. Slightly higher concentrations of endrin
have been detected in fish from the Hor al-Hammar Lake, with residue levels ranging
from 3 tg/kg in carp to 67 pg/kg wet weight in minnows. Endrin has not been detected
in the Arabian Gulf before, which may be due to the fact that this insecticide is relatively
short-living and has been used in few occasions in this region.
Although dieldrin has been officially banned in Iraq since 1976, its residues are expected
to persist owing to its long use for agricultural and public health purposes. However, resi-
due levels of dieldrin in the fish from the NW Arabian Gulf were at or near the detection
threshold of 1 tg/kg wet weight. More frequent residues of dieldrin were observed in the
Hor al-Hammar Lake. No significant difference (α = 0.05) in the residue levels between
fish types for lindane, α-endosulfan, p,p′-DDE, p,p′-DDT, and dieldrin was observed. The
aldrin levels in Nile perch ( Lates niloticus ) were significantly higher than the levels in Nile
tilapia ( Oreochromis niloticus ). No difference was observed in the distribution of residues in
the different parts of Nile tilapia, although a difference for p,p′-DDE was observed in the
Nile perch. No significant difference was observed in the average fat content of the tissue
of Nile perch and Nile tilapia; however, the distribution of fat was significantly different
in the different parts of the fish, with the abdominal portion having the highest amount of
fat. There was no correlation observed in this study between fat content and organochlo-
rine concentration. Lower p,p′-DDT residue levels as compared with the p,p′-DDE levels
observed indicate that DDT is no longer in use. The levels of OCP residues found in fish
samples were below the FAO, US FDA, Australian, and German extraneous residue limits
and maximum residue limits.
Lake Chicot is located in the alluvial plain of the Mississippi River in eastern Arkansas,
an area noted for its agricultural productivity. Because of the intensive agriculture in this
region, numerous organochlorine pesticides were applied for several decades to control
insect pests. Samples of fish from isolated and flow-through portions of Lake Chicot,
Arkansas, were analyzed for residual pesticide concentrations. DDT, and its metabolites,
and heptachlor were significantly (a = 0.05) higher in spotted gar ( Lepisosteus oculatus )
and yellow bullhead catfish ( Ictalurus natalis ) than in other species examined. Pesticide
concentrations did not exceed the acceptable levels established by the US Environmental
Protection Agency, although toxaphene levels in one white crappie ( Pomoxis annularis )
and one freshwater drum ( Aplodinotus grunniens ) were as high as 0.01 tg/kg. Bottom-
feeding and piscivorous fish had consistently higher concentrations of pesticides than fish
belonging to other feeding groups. The main body of the lake, with a large drainage area
(930 km 2 ) had higher concentrations of suspended solids than did the isolated northern
basin and produced fish with significantly (a = 0.05) higher levels of toxaphene, DDD, and
DDT. Insecticide concentrations were consistently greater in viscera with toxaphene, DDT,
DDE, and DDD levels significantly (a = 0.05) greater than in either whole fish or fish flesh
samples. Eight years after the ban, residual pesticides in fish from both basins of Lake
Chicot were still significantly (a = 0.05) higher during years of increased runoff, indicat-
ing the importance of watershed management practices in long-term downstream water
resources (Cooper and Knight 1987).
A study of the content of persistent OCPs (DDT and its metabolites, α-, β-, γ-isomers of
hexachlorocyclohexane) in the tissues and organs of some fish and molluskan species
from the lower reaches of the Tumen River and the contiguous part of Peter the Great
Bay (Sivuchya Bay and Zapadnaya Bay of the Furugelm) and Amursky bay showed
that the highest total content of HCHs (785.60 ng/g of gross mass) was revealed in the
digestive gland of the Japanese scallop Mizuhopecten yessoensis from Zapadnaya Bay
and in the brain and the liver of the starry flounder Platichthys stellatus from the Tumen