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Ascaris suum eggs were inactivated in distilled water and digested sludge by butanoic, pentanoic, and hexanoic acids. The fatty acids (short-chain fatty acids [SCFA]) were effective only when protonated and at sufficient concentrations. The conjugate bases were not effective at the concentrations evaluated. Predictions from an inhibition model (50% inhibitory concentration [IC 50 ]) based on quantitative structure-activity relationships were congruent with inactivation data.The nematode Ascaris lumbricoides releases highly resistant, unembryonated eggs into the environment, causing ϳ1.3 billion illnesses worldwide (12). The swine parasite Ascaris suum is routinely used as a surrogate for the human parasite (22) and is often found in sludges. Due to its resistance to biocontrol mechanisms (6) Ascaris is a model organism for developing environmentally safe disinfection methods (7,22). The eggs can be rendered nonviable through natural processes using extreme heat (Ͼ40°C) or with UV radiation (4). The use of short-chain fatty acids (SCFA) is another possible method of controlling Ascaris. The toxicity of SCFA to bacteria, e.g., Escherichia coli (9), Streptococcus, and Staphylococcus (20), fungi (14, 23), insects (15), and birds (13) a Letters after viability measurements denote statistically significant differences among the percentages of viable eggs when compared to the water controls which were conducted with each round of testing (data not shown). The overall average percent survival for the water controls was 90.3 Ϯ 2.7%. Data marked "a" were tested with the Proc Mix of SAS (P Ͻ 0.01). Data marked "b" were tested with the Student t test (P Ͻ 0.05). SD, standard deviation.b ND, not done.

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Microelectrophoresis is a common technique for probing the surface chemistry of the Cryptosporidium parvum oocyst. Results of previous studies of the electrophoretic mobility of C. parvum oocysts in which microelectrophoresis was used are incongruent. In this work we demonstrated that capillary electrophoresis may also be used to probe the surface characteristics of C. parvum oocysts, and we related the surface chemistry of C. parvum oocysts to their stability in water. Capillary electrophoresis results indicated that oocysts which were washed in a phosphate buffer solution had neutrally charged surfaces. Inactivation of oocysts with formalin did not influence their electrophoretic mobility, while oocyst populations that were washed in distilled water consisted of cells with both neutral and negative surface charges. These results indicate that washing oocysts in low-ionic-strength distilled water can impart a negative charge to a fraction of the oocysts in the sample. Rapid coagulation experiments indicated that oocysts did not aggregate in a 0.5 M NaCl solution; oocyst stability in the salt solution may have been the result of Lewis acid-base forces, steric stabilization, or some other factor. The presence of sucrose and Percoll could not be readily identified on the surface of C. parvum oocysts by attenuated total reflectance-Fourier transform infrared spectroscopy, suggesting that these purification reagents may not be responsible for the stability of the uncharged oocysts. These findings imply that precipitate enmeshment may be the optimal mechanism of coagulation for removal of oocysts in water treatment systems. The results of this work may help elucidate the causes of variation in oocyst surface characteristics, may ultimately lead to improved removal efficiencies in full-scale water treatment systems, and may improve fate and transport predictions for oocysts in natural systems.