A.C.S. Parr

The early stages of marine biofouling and its effect on two types of optical sensors

This paper records the results of an investigation into the effects of biofouling on optical marine sensors and the organisms responsible for the deterioration in sensor accuracy. Two kinds of commercial sub-surface optical marine sensor, commonly used to measure water quality, were operated in a natural marine environment and allowed to foul while measurements of the actual conditions were made daily using clean instruments. A number of glass and acrylic coupons were placed in the same environment and were removed at intervals throughout the trial. These coupons were examined and the biological population quantified. Deterioration in the optical properties of the coupons was measured using image analysis and UV-visible spectroscopy. The results from the coupons were compared with the results from the commercial instruments. It was observed that the major deterioration in instrumental accuracy occurred when a bacterial population exceeding 105/mm2 was found on the coupons. The algal population had little effect on the instruments over this time period. The acrylic coupons supported a lower fouling population, apparently due to the increased solubility of acrylic in seawater. The two optical techniques returned similar patterns of results for the surface area fouled, although the numerical values returned by each technique were different. Neither of these two techniques returned values directly comparable with the deterioration in accuracy of the commercial instruments. The trial took place on the Isle of Cumbrae in the Firth of Clyde on the west coast of Scotland, U.K.

An alternative approach to antifouling based on analogues of natural processes

A number of marine organisms are able to resist fouling pressure and remain essentially free of fouling. Some organisms are totally devoid of even the first stages of biofilm formation involving bacteria and microalgae. A key feature in recent research has been the realisation that previous low adherence technology is an insufficient technical solution and that natural models, based on marine and other organisms, incorporate other passive techniques for fouling resistance. These characteristics may be incorporated into physical analogues of the natural processes. This paper describes ways of producing physical analogues of some such characteristics, the application of such techniques to surfaces in the marine environment and the environmental impact. The paper includes some results of recent trials and a cost comparison.

The effect of benzalkonium chloride concentration on nine species of marine diatom

The effect of varying concentrations of benzalkonium chloride (BAK) on nine diatom species is measured, and related to the variation in tolerance levels of different species seen elsewhere in the literature. Different species showed different effective levels; however, all species were non-viable at 1×10−3% BAK. The technique being laboratory based and, therefore, immune from seasonal influences, is quick to perform and is easily adapted for bioassay work.

A novel technique to prevent bacterial fouling, using imposed surface potential

A. KERR, T. HODGKIESS, M.J. COWLING, C.M. BEVERIDGE, M.J. SMITH AND A.C.S. PARR. 1998. The effect of modest imposed surface potentials on the adhesion of marine bacteria to an electrically conducting layer deposited on silica glass is recorded. A positive shift increased bacterial settlement. However, a negative shift in potential was extremely beneficial in reducing numbers of adhered bacteria. An applied surface potential of − 66 mV SCE resulted in the bacterial population decreasing to approximately 12% of that on the uncharged reference sample. There was no further significant decrease in the adhered bacterial population when the magnitude of the negative potential was increased. The potential was maintained with very little current flow (less than 0·25 nA mm−2). The results were not due to any effect of the material used and therefore the technique could be useful for reducing bacterial fouling in many situations, including medical applications.

The non-toxic effects of a novel antifouling material on oyster culture

The production traits (size, weight, mortality and condition) of Crassostrea gigas oysters were examined when cultured in cages coated with a novel antifouling material consisting of a polymer film based on a hydrogel which had been loaded with the active material (benzalkonium chloride—BCl), a mixture of alkyldimethylbenzylammonium chlorides. Production traits of adult oysters and growth rate of larvae obtained from BCl-exposed adults were equal to the controls. Toxicity of BCl, as assessed by the oyster embryo bioassay, was two orders of magnitude lower than TBT and one order of magnitude lower than copper, the active compounds presently used in antifouling paints.

Some physical factors affecting the accumulation of biofouling

The effects of surface roughness and microsolubility on fouling levels are examined using glass and acrylic samples. It is found that both of these, often overlooked, physical characteristics have a noticeable effect on the rate of fouling. The microsolubility of acrylic results in lower fouling than found on glass despite the higher hydrophobicity of acrylic and the resultant increase in initial attraction for fouling organisms. Fouling levels were found to increase with increasing surface roughness and therefore studies on the fouling susceptibility of different materials should report the roughness values of the samples examined.

Optical assessment of a fouling‐resistant surface (PHEMA/ benzalkonium chloride) after exposure to a marine environment

A hydrogel based on poly(2-hydroxyethyl methacrylate) (PHEMA) containing benzalkonium chloride (BAK) can be used as an environmentally acceptable, fouling-resistant material in the marine environment. The loaded hydrogel system is transparent and has the potential to be used in the protection of optical ports in underwater instruments. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of the material after a marine exposure period. The optical transmittance of PHEMA/ BAK was higher for 10 weeks than that detected for poly(methyl methacrylate) (PMMA), a material currently used in commercial instruments, which confirmed the superior fouling resistance of the PHEMA/ BAK combination. The UV–vis spectroscopic method was quick, relatively cheap and accurate enough to allow the effects of the development of marine fouling on transparent surfaces for use in marine underwater optical applications to be monitored.