Pyrithiones are widely used as bactericides, fungicides, or algicides in a variety of products such as shampoos, metal working fluids, adhesives, sealants, and coatings. This broad antimicrobial activity, along with low water solubility and favorable environmental chemistry, makes zinc pyrithione and copper pyrithione potentially ideal replacements for TBT in marine antifouling paints. Several studies on the toxicity and environ- • mental fate of these pyrithiones have been conducted in freshwater and saltwater systems. Environmental fate studies show that pyrithiones rapidly degrade in the water column to less toxic compounds. Sediment accumulation is also prevented by the facile reduction of a critical functional group under anaerobic conditions. Modeling programs were used to calculate the predicted environmental concentration (PEC) for pyrithione. Comparison of PECs calculated for more persistent antifoulants with actual measured concentrations provided a measure of the bias inherent to the models. The results indicate a pyrithione risk quotient (PEC/PNEC) < 1. The findings are consistent with the absence of ecological effects during the long history of the use of zinc pyrithione as an antidandruff agent.

The environmental fate and the loss of toxicity of two important antifouling actives, zinc pyrithione (ZnPT) and copper pyrithione (CuPT), were investigated using a bioassay study and an outdoor microcosm study. The bioassay used inhibition of the growth of a marine diatom (Amphora coffeaeformis) to measure the toxicity of ZnPT and CuPT over time in sterile, natural, and sediment-supplemented seawater. In natural seawater and sediment-supplemented seawater in the dark and in sterile seawater exposed to light, growth inhibition was reduced at rates corresponding to the rapid degradation rates for ZnPT and CuPT measured in previous aquatic metabolism, die-away, and photolysis studies. Similarly, the bioassay results from sterile seawater in the dark were consistent with the slower degradation rates measured in abiotic hydrolysis studies. In addition to corroborating the rapid degradation of pyrithione upon exposure to light or sediment, the loss of toxicity indicated that the degradation products were not toxic at the concentrations produced from the dose, which was much higher than predicted environmental concentrations. To supplement environmental fate studies designed to elucidate single-pathway transformations, a microcosm study was conducted to integrate all of the degradation pathways. The study used two sediment and water systems, one of which was dosed during the day and the other at night. The pyrithione degraded rapidly in the water phase, with very little accumulation in the sediment. 2-Pyridine sulfonic acid (PSA) and carbon dioxide were the only detectable degradation products 30 d after dosing. Aquatic toxicity studies with PSA showed no observable effect at concentrations at least three orders of magnitude higher than those for either ZnPT or CuPT. As a result, the worst-case environmental concentration of PSA is expected to be far below the no observable effect concentration.

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Gradient index lenses were formed in a liquid-filled cavity supporting an ultrasonic standing wave. The constructed devices acted as diverging lenses or axicon lenses, depending on whether the center or edge region is interrogated. The focal length of the diverging lens was controllable with the frequency and amplitude of applied ultrasound from −100 mm to negative infinity. Experiments and models suggest that the primary process contributing to lensing is the steady-state density component of the finite-amplitude standing wave; sound amplitudes up to 150 MPa were calculated in glycerin, corresponding to a maximum contrast in the refractive on the order of 0.1%. This amplitude was also sufficient to move high index nanometer-scale particles via an acoustic radiation force and thereby create larger refractive index gradients. The segregation of suspended nanoparticles was found to enhance the lensing effects that occurred in the pure fluids. Concepts are also explored to manipulate the particle distribution in order to create converging lenses and/or other desirable optical components.

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