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With few exceptions, pesticides formulated as aqueous solutions and suspensions (flowables) require a preservative. Even most fungicide aqueous flowables require an effective bactericide. Preservatives are primarily incorporated to prevent (1) deterioration of sensitive formulation components (eg. rheological modifiers), and (2) formation of microbial slimes which can clog spray nozzles. The many requirements imposed on preservatives include (1) broad spectrum antimicrobial activity, (2) non-reactivity with other formulation components, (3) low phytotoxicity and mammalian toxicity, (4) activity over wide pH range, (5) high temperature stability, (6) ease of assay, (7) environmental safety, and (8) broad regulatory approvals. Considerable testing is required to determine the most cost-effective preservative level in each formulation.
Covered in this paper are (1) sources and control of contaminating organisms, (2) the importance of test organism adaptation and “challenge” testing in determining microbial susceptibility and optimal preservative level, and (3) comparison of several preservatives — including formaldehyde and 1,2-benzisothiazolin-3-one (active ingredient in PROXEL® GXL) — covered by EPA regulation 40 CFR 180.1001.
preservatives, pesticides, aqueous formulations, solutions, flowables, preservative requirements, microbial challenge testing, EPA regulatory considerations
Laboratory Supervisor, ICI Americas, Inc., Specialty Chemicals, Surfactants and Biocides Laboratories, Wilmington, DE