N., and Bakry, N. M. (2006)

Chem Codes: Chemical of Concern: PPB,CPY,DZ Rejection Code: EFFLUENT.

Anderson, B. S., Hunt, J. W., Phillips, B. M., Nicely, P. A., Gilbert, K. D., DeVlaming, V., Connor, V., Richard, N., and Tjeerdema, R. S. ( 2003). Ecotoxicologic impacts of agricultural drain water in the Salinas River, California, USA. Environmental Toxicology and Chemistry [Environ. Toxicol. Chem.]. Vol. 22, no. 10, pp. 2375-2384. Oct 2003.

Chem Codes: Chemical of Concern: DZ Rejection Code: EFFLUENT.

ISSN: 0730-7268

Descriptors: Pesticides
Descriptors: Watersheds
Descriptors: Diazinon
Descriptors: turbidity
Descriptors: Community structure
Descriptors: Pollution effects
Descriptors: Pore water
Descriptors: Sediments
Descriptors: chlorpyrifos
Descriptors: Toxicity
Descriptors: Agriculture
Descriptors: Ecosystem disturbance
Descriptors: Drainage
Descriptors: Agricultural Runoff
Descriptors: Drainage Water
Descriptors: Rivers
Descriptors: Macroinvertebrates
Descriptors: Sediment Contamination
Descriptors: Crustaceans
Descriptors: Interstitial Water
Descriptors: Amphipods
Descriptors: Agricultural Watersheds
Descriptors: Acute Toxicity
Descriptors: Toxicity tests
Descriptors: Zoobenthos
Descriptors: Sediment pollution
Descriptors: Agricultural pollution
Descriptors: Community composition
Descriptors: Sediment-water interface
Descriptors: Mortality causes
Descriptors: River water
Descriptors: Lethal limits
Descriptors: Sediment chemistry
Descriptors: Ceriodaphnia dubia
Descriptors: Hyalella azteca
Descriptors: Azteca
Descriptors: USA, California, Salinas R.
Abstract: The Salinas River is the largest of the three rivers that drain into the Monterey Bay National Marine Sanctuary in central California (USA). Large areas of this watershed are cultivated year-round in row crops, and previous laboratory studies have demonstrated that acute toxicity of agricultural drain water to Ceriodaphnia dubia is caused by the organophosphate (OP) pesticides chlorpyrifos and diazinon. We investigated chemical contamination and toxicity in waters and sediments in the river downstream of an agricultural drain water input. Ecological impacts of drain water were investigated by using bioassessments of macroinvertebrate community structure. Toxicity identification evaluations were used to characterize chemicals responsible for toxicity. Salinas River water downstream of the agricultural drain was acutely toxic to the cladoceran Ceriodaphnia dubia, and toxicity to C. dubia was highly correlated with combined toxic units (TUs) of chlorpyrifos and diazinon. Laboratory tests were used to demonstrate that sediments in this system were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. Toxicity identification evaluations (TIEs) conducted on sediment pore water suggested that toxicity to amphipods was due in part to OP pesticides; concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d mean lethal concentration (LC50) for H. azteca. Potentiation of toxicity with addition of the metabolic inhibitor piperonyl butoxide suggested that sediment toxicity also was due to other non-metabolically activated compounds. Macroinvertebrate community structure was highly impacted downstream of the agricultural drain input, and a number of macroinvertebrate community metrics were negatively correlated with combined TUs of chlorpyrifos and diazinon, as well as turbidity associated with the drain water. Some macroinvertebrate metrics were also correlated with bank vegetation cover. This study suggests that pesticide pollution is the likely cause of ecological damage in the Salinas River, and this factor may interact with other stressors associated with agricultural drain water to impact the macroinvertebrate community in the system.
Language: English
English
Publication Type: Journal Article
Environmental Regime: Freshwater
Classification: P 2000 FRESHWATER POLLUTION
Classification: SW 3030 Effects of pollution
Classification: AQ 00008 Effects of Pollution
Classification: Q5 01504 Effects on organisms
Classification: EE 40 Water Pollution: Monitoring, Control & Remediation
Subfile: Water Resources Abstracts; Aqualine Abstracts; ASFA 3: Aquatic Pollution & Environmental Quality; Environmental Engineering Abstracts; Pollution Abstracts

Anderson, B. S., Hunt, J. W., Phillips, B. M., Nicely, P. A., Vlaming, V. de, Connor, V., Richard, N., and Tjeerdema, R. S. (2003). Integrated assessment of the impacts of agricultural drainwater in the Salinas River (California, USA). Environmental Pollution 124: 523-532.

Chem Codes: Chemical of Concern: DZ Rejection Code: EFFLUENT.

The Salinas River is the largest of the three rivers that drain into the Monterey Bay National Marine Sanctuary in central California. Large areas of this watershed are cultivated year-round in row crops and previous laboratory studies have demonstrated that acute toxicity of agricultural drainwater to Ceriodaphnia dubia is caused by the organophosphate (OP) pesticides chlorpyrifos and diazinon. In the current study, we used a combination of ecotoxicologic tools to investigate incidence of chemical contamination and toxicity in waters and sediments in the river downstream of a previously uncharacterized agricultural drainage creek system. Water column toxicity was investigated using a cladoceran C. dubia while sediment toxicity was investigated using an amphipod Hyalella azteca. Ecological impacts of drainwater were investigated using bioassessments of macroinvertebrate community structure. The results indicated that Salinas River water downstream of the agricultural drain is acutely toxic to Ceriodaphnia, and toxicity to this species was highly correlated with combined toxic units (TUs) of chlorpyrifos and diazinon. Laboratory tests were used to demonstrate that sediments in this system were acutely toxic to H. azteca, which is a resident genus. Macroinvertebrate community structure was moderately impacted downstream of the agricultural drain input. While the lowest macroinvertebrate abundances were measured at the station demonstrating the greatest water column and sediment toxicity and the highest concentrations of pesticides, macroinvertebrate metrics were more significantly correlated with bank vegetation cover than any other variable. Results of this study suggest that pesticide pollution is the likely cause of laboratory-measured toxicity in the Salinas River samples and that this factor may interact with other factors to impact the macroinvertebrate community in the system. Chlorpyrifos/ Diazinon/ Toxicity/ Sediments/ Macroinvertebrates

Anderson, J. F. and Wojtas, M. A. (1986). Honey bees (Hymenoptera: Apidae) contaminated with pesticides and polychlorinated biphenyls. Journal of economic entomology [j. Econ. Entomol.] 79: 1200-1205.
Chem Codes: Chemical of Concern: MOM Rejection Code: SURVEY.

Abstract: Multiple pesticides were simultaneously present in dead honey bees, Apis mellifera L., or in brood comb in 28 of 55 poisoned apiaries in Connecticut in 1983-85. Methyl parathion (Penncap-M), carbaryl, and endosulfan were each detected in 34, 33, and 13 of the apiaries, respectively. Less frequently detected pesticides were methomyl, chlordane, diazinon, captan, and malathion. Health of colonies poisoned with methyl parathion only or methyl parathion in combination with other insecticides was often severely affected, whereas colonies affected by carbaryl only or carbaryl plus insecticides other than methyl parathion often recovered. Arocolor 1248 and 1260 (polychlorinated biphenyls) were detected in dead bees, brood comb, honey comb, or honey. Detectable quantities of polychlorinated biphenyls less than or equal to 0.80 ppm were in 4 of 71 honey samples.

Anderson, T. D. and Lydy, M. J. *. (2002). Increased toxicity to invertebrates associated with a mixture of atrazine and organophosphate insecticides. Environmental Toxicology and Chemistry [Environ. Toxicol. Chem.]. Vol. 21, no. 7, pp. 1507-1514. Jul 2002.
Chem Codes: Chemical of Concern: DZ Rejection Code: MIXTURE.

ISSN: 0730-7268

Descriptors: Atrazine
Descriptors: Invertebrata
Descriptors: Toxicity
Descriptors: Organophosphates
Descriptors: Mortality
Descriptors: Lethal dose
Descriptors: Pesticides (organophosphorus)
Descriptors: Chlorpyrifos
Descriptors: Methyl parathion
Descriptors: Diazinon
Descriptors: Toxicity testing
Descriptors: Hyalella azteca
Descriptors: Musca domestica
Abstract: This study examined the joint toxicity of atrazine and three organophosphate (OP) insecticides (chlorpyrifos, methyl parathion, and diazinon) exposed to Hyalella azteca and Musca domestica. A factorial design was used to evaluate the toxicity of binary mixtures in which the lethal concentration/lethal dose (LC1/LD1, LC5/LD5, LC15/LD15, and LC50/LD50) of each OP was combined with atrazine concentrations of 0, 10, 40, 80, and 200 mu g/L for H. azteca and 0, 200, and 2,000 ng/mg for M. domestica. Atrazine concentrations ( greater than or equal to 40 mu g/L) in combination with each OP caused a significant increase in toxicity to H. azteca compared with the OPs dosed individually. Acetylcholinesterase (AChE) activity also was examined for the individual OPs with and without atrazine treatment. Atrazine in combination with each of the OPs resulted in a significant decrease in AChE activity compared with the OPs dosed individually. In addition, H. azteca that were pretreated with atrazine ( greater than or equal to 40 mu g/L) were much more sensitive to the OP insecticides compared with H. azteca that were not pretreated with atrazine before being tested. Topical exposure to atrazine concentrations did not significantly increase OP toxicity to M. domestica. The results of this study indicate the potential for increased toxicity in organisms exposed to environmental mixtures.
Language: English
English
Publication Type: Journal Article
Classification: P 5000 LAND POLLUTION
Classification: X 24131 Acute exposure
Classification: Z 05183 Toxicology & resistance
Subfile: Pollution Abstracts; Toxicology Abstracts; Entomology Abstracts

Anees, M. A. (1974). Changes in Starch-Gel Electrophoretic Pattern of Serum Proteins of a Freshwater Teleost Channa punctatus (Bloch), Exposed to Sublethal and Chronic Levels of Three Organophosphorus Insecticides. Ceylon J.Sci.Biol.Sci. 11: 53-57 (Used 5648 As Reference).

EcoReference No.: 5988

Chemical of Concern: DMT,DZ,MP; Habitat: A; Effect Codes: BCM; Rejection Code: NO ENDPOINT(ALL CHEMS).

Anees, M. A. (1978). Haematological Abnormalities in a Freshwater Teleost, Channa punctatus (Bloch), Exposed to Sublethal and Chronic Levels of Three Organophosphorus Ins. Int.J.Ecol.Environ.Sci. 4: 53-60.

EcoReference No.: 6960

Chemical of Concern: DMT,DZ,MP; Habitat: A; Effect Codes: BCM,CEL; Rejection Code: NO ENDPOINT(ALL CHEMS).

Anees, M. A. (1978). Hepatic Pathology in a Fresh-Water Teleost Channa punctatus (Bloch) Exposed to Sub-lethal and Chronic Levels of Three Organophosphorus Insecticides. Bull.Environ.Contam.Toxicol. 19: 524-527.

EcoReference No.: 6099

Chemical of Concern: DMT,DZ,MP; Habitat: A; Effect Codes: CEL; Rejection Code: NO ENDPOINT,CONTROL(ALL CHEMS).

Anees, M. A. (1976). Intestinal Pathology in a Freshwater Teleost, Channa punctatus (Bloch) Exposed to Sub-lethal and Chronic Levels of Three Organophosphorus Insecticides. Acta Physiol.Latinoam. 26: 63-67.

EcoReference No.: 6100

Chemical of Concern: DMT,DZ,MP; Habitat: A; Effect Codes: CEL; Rejection Code: NO ENDPOINT(ALL CHEMS).

Angelidis, M. O., Markantonatos, P. G., Bacalis, N. C., and Albanis, T. A. (1996). Seasonal fluctuations of nutrients and pesticides in the basin of Evrotas river, Greece. Journal of Environmental Science and Health Part a Environmental Science and Engineering & Toxic and Hazardous Substance Control 31 : 387-410.

Chem Codes: SZ,MTL,CBF Rejection Code: NO SPECIES.

ABSTRACT: BIOSIS COPYRIGHT: BIOL ABS. Water and sediment samples from several stations along the Evrotas river, were collected for one year period, from August 1991 to August 1992, and were analysed for nutrients (Total N, NO3-N and Total P) and pesticides. Higher nutrient concentrations were detected in the part of the river which is flowing through the plain of Sparta and is receiving industrial and domestic effluents, as well as the runoff from the agricultural land of the area. The industrial effluents (orange juice plants) and the agricultural land runoff, seem to play the major role during winter and spring, while the discharge of domestic septage (cesspools contents) in the reduced water flow, appears to be an important source of nutrient pollution during summer, In the water and sediments of the river were detected the herbicides alachlor, atrazine, amitrol and simazine, the insecticides azinphos ethyl, carbofuran, diazinon, dicofol, endosulfan, fenthion, methyl parathion, as well as the fungicide c

KEYWORDS: Ecology
KEYWORDS: Ecology
KEYWORDS: Biochemical Studies-General
KEYWORDS: Toxicology-Environmental and Industrial Toxicology
KEYWORDS: Public Health: Environmental Health-Sewage Disposal and Sanitary Measures
KEYWORDS: Public Health: Environmental Health-Air
KEYWORDS: Pest Control

Angelidis, M. O., Markantonatos, P. G., Bacalis, N. C., and Albanis, T. A. (1996). Seasonal fluctuations of nutrients and pesticides in the basin of Evrotas River, Greece. J. ENVIRON. SCI. HEALTH, PART A: ENVIRON. SCI. ENG. TOXIC HAZARD. SUBST. CONTROL. Vol. A31, no. 2, pp. 387-340. 1996.

Chem Codes: Chemical of Concern: DZ Rejection Code: SURVEY.

ISSN: 0360-1266

Descriptors: nutrients
Descriptors: pesticides
Descriptors: water sampling
Descriptors: rivers
Descriptors: industrial wastewater
Descriptors: seasonal variations
Descriptors: domestic wastewater
Descriptors: agricultural runoff
Descriptors: nutrient concentrations
Descriptors: industrial effluents
Descriptors: pollution monitoring
Descriptors: nutrients (mineral)
Descriptors: river water
Descriptors: Greece, Evrotas R.
Abstract: Water and sediment samples from several stations along the Evrotas River, were collected for one year period, from August 1991 to August 1992, and were analysed for nutrients (Total N, NO sub(3)-N and Total P) and pesticides. Higher nutrient concentrations were detected in the part of the river which is flowing through the plain of Sparta and is receiving industrial and domestic effluents, as well as the runoff from the agricultural land of the area. The industrial effluents (orange juice plants) and the agricultural land runoff, seem to play the major role during winter and spring, while the discharge of domestic septage (cesspools contents) in the reduced water flow, appears to be an important source of nutrient pollution during summer. In the water and sediments of the river were detected the herbicides alachlor, atrazine, amitrol and simazine, the insecticides azinphos ethyl, carbofuran, diazinon, dicofol, endosulfan, fenthion, methyl parathion, as well as the fungicide captan. In the river water, the highest concentrations of herbicides atrazine, simazine and alachlor were found in summer (August 1991). The same herbicides as well as the insecticides azinphos ethyl, diazinon, dicofol, fenthion and methyl parathion, were found in significant amounts in the riverine sediments.
Language: English
English
Publication Type: Journal Article
Environmental Regime: Freshwater
Classification: SW 3020 Sources and fate of pollution
Classification: P 2000 FRESHWATER POLLUTION
Classification: Q5 01505 Prevention and control
Subfile: ASFA 3: Aquatic Pollution & Environmental Quality; Pollution Abstracts; Water Resources Abstracts

Anjum, F. and Siddiqui, M. K. J. (1990). In Vitro Inhibition of Fish (Tilapia mossambica) Brain Ca2+ -ATPase by Monocrotophos, Dimethoate, Diazinon and DDT. Indian J.Exp.Biol. 28: 488-489.

Chem Codes: EcoReference No.: 45841
Chemical of Concern: DZ,DMT,DDT Rejection Code: IN VITRO.

ANJUM, F. and SIDDIQUI, M. KJ (1990). In vitro inhibition of fish (Tilapia mossambica) brain calcium-ATPase by monocrotophos, dimethoate, diazinon and DDT. INDIAN J EXP BIOL; 28 488-489.

Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

BIOSIS COPYRIGHT: BIOL ABS. Fish brain Ca2+-ATPase was most sensitive to DDT followed by dimethoate > monocrotophos > diazinon. It is suggested that these organophosphorus pesticides besides inhibiting acetylcholinesterase also inhibit Ca2+-ATPase during neurotoxicological events. Biochemistry/ Nucleic Acids/ Purines/ Pyrimidines/ Amino Acids/ Peptides/ Proteins/ Minerals/ Enzymes/Physiology/ Diagnosis/ Nervous System/ Nervous System/Physiology/ Nervous System/Metabolism/ Nervous System Diseases/Pathology/ Poisoning/ Animals, Laboratory/ In Vitro/ Tissue Culture/ Herbicides/ Pest Control/ Pesticides/ Fishes

Anon. (1999). Diazinon Sources in Runoff From the San Francisco Bay Region. Watershed Protection Techniques [Watershed Prot. Tech.]. Vol. 3, no. 1, pp. 613-616. Apr 1999.
Chem Codes: Chemical of Concern: DZ Rejection Code: SURVEY.

ISSN: 1073-9610

Descriptors: Water Pollution Sources
Descriptors: Nonpoint Pollution Sources
Descriptors: Watershed Management
Descriptors: Pesticides
Descriptors: Diazinon
Descriptors: Toxicity
Descriptors: Ecological Effects
Descriptors: Path of Pollutants
Descriptors: Runoff
Descriptors: Insecticides
Descriptors: Water pollution
Descriptors: Watersheds
Descriptors: River basin management
Descriptors: Pollution detection
Descriptors: Ceriodaphnia dubia
Descriptors: INE, USA, California, San Francisco Bay
Abstract: Diazinon is a common broad spectrum insecticide that is widely applied by homeowners and pest control professionals alike. In California alone, diazinon is contained in over 200 different pesticide formulations. The primary use for diazinon is for general insect control, with the most common targets being ants, fleas, ticks, grubs and spiders. It is often the insecticide of choice to deal with fire ant problems in the South. There are several reasons why watershed managers are concerned about the use of diazinon. To begin with, diazinon is highly toxic to aquatic life at exceptionally low levels. Toxicologists have found that diazinon causes mortality in the popular bioassay organism, Ceriodaphnia dubia (water flea) at exposure levels as low as 300 parts per trillion. In addition, diazinon is very soluble and therefore very mobile in the urban environment. Although it eventually breaks down in the environment, diazinon has a half-life of about 40 days in surface waters. In addition, diazinon is typically sprayed as a concentrate on a spot basis near foundations, driveway cracks, sidewalk crevices and other impervious surfaces.
Language: English
English
Publication Type: Journal Article
Environmental Regime: Marine
Classification: SW 3020 Sources and fate of pollution
Classification: Q5 01503 Characteristics, behavior and fate
Classification: EE 40 Water Pollution: Monitoring, Control & Remediation
Classification: SW 3030 Effects of pollution
Subfile: ASFA 3: Aquatic Pollution & Environmental Quality; Environmental Engineering Abstracts; Water Resources Abstracts

ANON (1985). REPORT OF THE WORKING GROUP OF THE PLANNING COMMISSION ON PESTICIDES INDUSTRY FOR THE SEVENTH FIVE YEAR PLAN. PESTICIDES (BOMBAY); 19 (9). 1985 (RECD. 1986). 11-20.

Chem Codes: Chemical of Concern: DZ Rejection Code: NO TOX DATA.

BIOSIS COPYRIGHT: BIOL ABS. RRM AGRICHEMICAL SUPPLY INDUSTRY AGRICHEMICAL SERVICE INDUSTRY AGRIBUSINESS INDIA Grasses/Growth & Development/ Soil/ Plant Diseases/ Preventive Medicine/ Herbicides/ Pest Control/ Pesticides

Anonymous (1972). Diazinon. In: Tech.Bull., CIBA-BEIGY, Agric.Div., Ardsley, NY 10 p.
Chem Codes: Chemical of Concern: DZ Rejection Code: NO CITATION/REVIEW.

Anonymous ( Occupational Safety And Health Guidelines For Chemical Hazards. Supplement Iv-Ohg.

Chem Codes: CHLOR Rejection Code: HUMAN HEALTH.

revised occupational safety and health guidelines were provided for the following chemicals: benzidine (92875), tert-butyl-chromate (1189851), calcium-oxide (1305788), synthetic camphor (76222), carbaryl (63252), chlorobenzene (108907), o-chlorobenzylidene-malononitrile (2698411), chloropicrin (76062), decaborane (17702419), and portland cement. new guidelines were presented for: calcium-carbonate (471341), calcium-cyanamide (156627), calcium-hydroxide (1305620), calcium-silicate (1344952), caprolactam (105602) dust and vapor, captafol (2425061), captan (133062), carbofuran (1563662), carbon-tetrabromide (558134), carbon-tetrachloride (56235), carbonyl-fluoride (353504), catechol (120809), cellulose (9004346), cesium-hydroxide (21351791), chloroacetyl-chloride (79049), chlorodifluoromethane (75456), chloropentafluoroethane (76153), chlorpyrifos (2921882), o-chlorostyrene (2039874), 2-chloro-6-trichloromethyl-pyridine (1929824), o-chlorotoluene (95498), clopidol (2971906), cobalt-carbonyl (10210681), cobalt-hydrocarbonyl (16842038), crufomate (299865), cyanogen (460195), cyanogen-chloride (506774), cyclohexylamine (108918), cyclonite (121824), cyclopentane (287923), diazinon (333415), 2-n-dibutylaminoethanol (102818), dichloroacetylene (7572294), 1,3-dichloropropene (542756), 2,2-dichloropropionic-acid (75990), dicrotophos (141662), dicyclopentadiene (77736), dicyclopentadienyl-iron (102545), diethanolamine (111422), diethylenetriamine (111400), diethyl-phthalate (84662), dinitolmide (148016), dipropyl-ketone (123193), disulfiram (97778), diuron (330541), endosulfan (115297), ethion (563122), ethylene-glycol (107211), and ethylidene-norbornene (16219753). dcn-230737/ niosh publication/ biological monitoring/ chemical industry workers/ personal protective equipment/ respiratory protection/ toxic materials/ air quality monitoring/ medical screening/ hazardous waste cleanup

ANONYMOUS (1999). This meeting contains abstracts of 42 papers, written in English, covering chemical studies of toxic substances and experimental studies in animals and tissue culture, including enzymology. JOURNAL OF HEALTH SCIENCE; 45 (1). 1999. P.1-P.42.
Chem Codes: Chemical of Concern: DZ Rejection Code: ABSTRACT.

BIOSIS COPYRIGHT: BIOL ABS. This meeting contains abstracts of 42 papers, written in English, covering chemical studies of toxic substances and experimental studies in animals and tissue culture, including enzymology. Congresses/ Biology/ Biochemistry/ Coenzymes/ Comparative Study/ Enzymes/ Poisoning/ Animals, Laboratory/ Animals

Antharavally, B., Tepp, W., and DasGupta, B. R. *. (1998). Status of Cys residues in the covalent structure of botulinum neurotoxin types A, B, and E. Journal of Protein Chemistry [J. Protein Chem.]. Vol. 17, no. 3, pp. 187-196. Apr 1998.
Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

ISSN: 0277-8033

Descriptors: Botulism
Descriptors: Toxins
Descriptors: Neurotoxins
Descriptors: Disulfide bonds
Descriptors: Cysteine
Descriptors: Clostridium botulinum
Abstract: Clostridium botulinum neurotoxin (NT) serotypes A, B, and E have 9, 10, and 8 Cys residues, respectively, as deduced from nucleotide sequences. Each of the 150-kDa NTs has at least one disulfide; but type B, like types A and E, may have two disulfides. Using two different chemical reagents, we studied the status of the Cys residues in these three proteins after (i) the final anion exchange chromatographic step in their purification (fresh NT), (ii) 24 hr storage at 8 degree C, (iii) precipitation with ammonium sulfate (precipitated NT), and (iv) dissolving the precipitated NT in 6 M guanidine-HCl. In all three NT serotypes the number of Cys residues titrated with 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) as free -SH groups varied, depending upon the absence or presence of EDTA added to the chromatography buffer, storage condition, age, and presence of the denaturant. Titration of 9.5-10 and 5.4-6.0 -SH groups in fresh NTs type B and E, respectively, indicated total and partial absence of disulfide bonds. Fewer titratable -SH groups in the precipitated NT than in the fresh NT suggested formation of disulfide and/or inaccessibility of the -SH groups due to protein's conformational change(s). When the precipitated NTs were dissolved in 6 M guanidine times HCl, in the absence of any added reducing agent, all Cys residues of types B and E, and 6.4-8.3 Cys in type A NT were titratable with DTNB. Iodoacetamide modification of precipitated NT types A, B, and E carboxymethylated 4, 2, and 2 Cys residues, respectively; these numbers rose to 6, 9.4, and 8 when these proteins were carboxymethylated after dissolving in 6 M guanidine-HCl in the absence of any added reducing agent. We propose that -S-S- cleavage mediated by the -SH/-S-S- exchange observed in vitro after unfolding the NTs (also unfolded by 2 M guanidine-HCl or urea) possibly mimicks a similar exchange process inside the endosomes, where the NTs are thought to undergo conformational changes, resulting in the reductive cleavage of the interchain disulfide between the 50-kDa light and 100-kDa heavy chain, which in turn releases the light chain and allows its egress out of the endosomes into the cytosol.