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Biological Exposure Indices (BEI) [ACGIH] - Acetylcholinesterase activity in red blood cells = 70% of individual's baseline; Butylcholinesterase activity in serum or plasma = 60% of individual's baseline; Sample at end of shift; [TLVs and BEIs]

SRP: At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.

Excerpt from ERG Guide 151 [Substances - Toxic (Non-Combustible)]:

FOR PROTECTION DURING APPLICATION WEAR HAT, LONG-SLEEVED SHIRT, TROUSERS. IN ADDITION, MIXER/LOADERS MUST WEAR RUBBER OR NEOPRENE GLOVES.

TERRESTRIAL FATE: If released on soil, merphos would be expected to adsorb strongly to soil(1,SRC) and be oxidized to S,S,S-tributyl phosphorotrithioate (DEF)(2).

AQUATIC FATE: If released in water, merphos will be oxidized to S,S,S-tributyl phosphorotrithioate (DEF). In th Little Miami River, complete oxidation to DEF occurred within an hour(1). The fact that merphos is expected to adsorb strongly to particulate matter in the water column (estimated Koc of 62,000 from structure(2)), apparently did not impede its oxidation(SRC).

ATMOSPHERIC FATE: If released into the atmosphere during spraying operations, merphos will exist as an aerosol and be removed by gravitational settling and be readily oxidized to S,S,S-tributyl phosphorotrithioate (DEF) in the drifting spray(2). Vapor-phase merphos will react with photochemically-produced hydroxyl radicals, with an estimated half-life of 4.9 hr(1).

Merphos was detected in food in FDA's adult Total Diet Study in FY78-82(1). While the commodity group, number of detections and concentration levels were not reported, fewer than 10 of the 1044 composite samples contained the pesticide(1). Merphos was detected in 9 of 6391 domestic agricultural commodities during surveillance sampling between FY82 and FY86(2). The distribution of the residue concentrations were (concentration range in ppm, number): 0.05-0.10, 1; 0.10-0.50, 3; 0.50-1.0, 2; >2.0, 3(2). Of these, 7 samples exceeded EPA's tolerance(2). During the same time period, merphos residues were not found in samples of 12,044 imported agricultural commodities(2).

Merphos

Nervous

3 x 10 ^-5 mg/kg-day

Merphos was found in only 1 of 2479 (0.04%) air samples taken between 1970 and 1972 as part of a national pesticide air monitoring program(1). The positive sample contained 8.8 ng/cu m of merphos and was from North Memphis, TN in 1971(1) and was 275 m from a formulation plant(2).

A CASE OF DELAYED NEUROTOXICITY IN 28-YR-OLD MAN WHO ACCIDENTALLY SPLASHED MERPHOS ON HIS BARE ARMS OVER A PERIOD OF 3 DAYS WHILE WORKING WITH THE DEFOLIANT. APPROX 14 DAYS AFTER EXPOSURE, COMPLETE FACIAL DIPLEGIA DEVELOPED. ELECTROMYOGRAPHY DEMONSTRATED DECREASED VOLTAGE OF MUSCLE ACTION POTENTIAL, DELAYED CONDUCTION VELOCITY IN MOTOR NERVE FIBERS, INCREASED INSERTIONAL ACTIVITY, AND DENERVATION POTENTIALS. HE RECOVERED COMPLETELY.

S,S,S-Tributyl phosphorotrithioate and merphos can produce delayed neurotoxicity in animals. Inhibition of the neurotoxic esterase in lymphocytes was measured in 7 workers exposed during aerial and ground application of these defoliants on cotton fields as was peripheral nerve function. The major route of exposure was via the skin. Lymphocyte neurotoxic esterase was affected in exposed workers according to both intensity and length of exposure. There were no detectable electrophysiological effects. Measurement of neurotoxic esterase in lymphocytes in workers exposed to organophosphates is a rational biomonitor of delayed neuropathy.

Merphos will be released to the environment as a result of its use as a defoliant on cotton preparatory to machine harvesting(1,2) for which it is used as an aqueous emulsion(3). It may also be released during its production, transport, formulation, and disposal.

Using an estimated log Kow of 7.67(1), one would estimate a BCF of 40,000 for merphos using a recommended regression equation(2). This would indicate that merphos would bioconcentrate in aquatic organisms. However, merphos' rapid oxidation in water would suggest little tendency to bioconcentrate(SRC).

As the federal pesticide law FIFRA directs, EPA is conducting a comprehensive review of older pesticides to consider their health and environmental effects and make decisions about their future use. Under this pesticide reregistration program, EPA examines health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether they are eligible for reregistration. In addition, all pesticides must meet the new safety standard of the Food Quality Protection Act of 1996. Pesticides for which EPA had not issued Registration Standards prior to the effective date of FIFRA, as amended in 1988, were divided into three lists based upon their potential for human exposure and other factors, with List B containing pesticides of greater concern and List D pesticides of less concern. Merphos is found on List B. Case No: 2385; Pesticide type: Fungicide, herbicide; Case Status: No products containing the pesticide are actively registered ... The case /is characterized/ as "cancelled." Under FIFRA, pesticide producers may voluntarily cancel their registered products. EPA also may cancel pesticide registrations if registrants fail to pay required fees or make/meet certain reregistration commitments, or if EPA reaches findings of unreasonable adverse effects.; Active ingredient (AI): Tributyl phosphorotrithioite; AI Status: The active ingredient is no longer contained in any registered pesticide products ... "cancelled."