Water microlayers

In aquatic environments, organotin concentrations were elevated in sediments, biota, and surface water microlayers collected near marinas, aquaculture rearing pens, and other facilities where organotin-based antifouling paints were used. In some cases, organotin concentrations in the water... 

Sodergren A, Larsson P, Knulst J, et al. 1990. Transport of incinerated organochlorine compounds to air, water, microlayer, and organisms. Marine Pollut Bull 21 18-24. 

In aquatic environments, organotin concentrations were elevated in sediments, biota, and surface water microlayers collected near marinas, aquaculture rearing pens, and other facilities where organotin-based antifouling paints were used. In some cases, organotin concentrations in the water column were sufficiently high to pose a substantial risk to sensitive species. Data are limited on concentrations of organotins in environmental samples, especially in samples from terrestrial ecosystems, and this may be attributed, in part, to limitations in routine chemical analytical capabilities. 

Because of their hydrophobic nature, siUcones entering the aquatic environment should be significantly absorbed by sediment or migrate to the air—water interface. SiUcones have been measured in the aqueous surface microlayer at two estuarian locations and found to be comparable to levels measured in bulk (505). Volatile surface siloxanes become airborne by evaporation, and higher molecular weight species are dispersed as aerosols. 

Diisopropyl methylphosphonate is slightly soluble in water (0.1—0.3 g/L at 25°) and has been demonstrated in laboratory studies to quickly diffuse between the surface microlayer into the water column after deposition as aerosols on fresh water (Van Voris et al. 1987). The solubility of diisopropyl methylphosphonate was 80 g/L (8%) and remained in solution even when the temperature was lowered to freezing (Bucci et al. 1997). In addition, there was no significant loss of diisopropyl methylphosphonate from the water column to the atmosphere, in either the presence or absence of a light wind over the water surface. Human exposure resulting from the vaporization of diisopropyl methylphosphonate from surface water is considered insignificant (EPA 1989). 

Evaporation-of-microlayer theory. A later hypothesis for the mechanism of nucleate boiling considers the vaporization of a micro layer of water underneath the bubble. This was first suggested by Moore and Mesler (1961), who measured... 

Estimation of microlayer evaporation The model, incorporating the evaporation from a microlayer surf ace underneath a bubble attached to the heater surf ace, was used by Hendricks and Sharp (1964). With water as the fluid, at somewhat subcooled conditions, the heat transfer rates were as high as 500,000 Btu/hr ft2, or... 

Determination of the persistence and mobility of organotin compounds — especially in aquatic abiotic materials, such as sediments, sediment interstitial waters, suspended particulates, and the water column — and on the partitioning of these compounds between the surface microlayer and subsurface waters (Wilkinson 1984 Thompson et al. 1985). 

Cleary, J.J. and A.R.D. Stebbing. 1987. Qrganotin in the surface microlayer and subsurface waters of southwest England. Mar. Pollut. Bull. 18 238-246. 

All but the most heavily contaminated fresh and marine waters contain total PAH concentrations in the part-per-trillion or low part-per-billion range (Table 25.3) (Neff 1982b). A large proportion of the PAH content in water is probably adsorbed onto suspended solids (Harrison et al. 1975). In Lake Michigan, concentrations of total PAHs in the surface microlayer varied from 0.15 to 0.45 pg/L, representing on a relative scale, 106 times the concentration in air, suggesting that aerosols are a major source of these compounds and that the microlayer is a repository until the PAHs are removed by adsorption and sedimentation (Strand and Andren 1980). 

Consequently, for an accurate quantification of surfactants in the water column, sampling must be performed by taking surface microlayer samples (at depths between 0 and 3—5 mm), using a surface sampler, and at various greater depths with Ruttner or similar bottles. 

The proportion of long-chain LAS homologues is greater in the solid phase (solids in suspension and sediment) than in water and greater than in commercial LAS. For LAS clear vertical trends in distribution can be observed both in the water and sediment columns, with relatively enriched concentrations in the surface microlayer and sediment top layers. 

Booij, K. and van Drooge, B.L. 2001, Polychlorinated biphenyls andhexachlorobenzene in atmosphere, sea-surface microlayer, and water measured widi semi-permeable membrane devices (SPMDs). Chemosphere 44 91—98. 

SauerTC Jr, Durell GS, Brown JS, et al. 1989. Concentrations of chlorinated pesticides and PCBs in microlayer and seawater samples collected in open-ocean waters off the U.S. East Coast and in the Gulf of Mexico. Mar Chem 27 235-257. 

DOM also tends to be concentrated at boimdaries, such as the sediment-water and air-sea interfeces. The latter is also characterized by enrichments of POM, such as bacteria. Under calm conditions, the DOM and POM that collects at the air-sea interface forms a visible surfece slick or microlayer. On windy days, this organic matter can be whipped up into an emulsion that has the appearance of a very sturdy foam. DOM can also be transferred into the POM pool by adsorbing onto organic particles. 

Gearing PJ, Gearing IN. 1982b. Transport of no. 2 fuel oil between water column, surface microlayer and atmosphere in controlled ecosystems. Marine Environmental Research 6(2) 133-143. 

L. Manodori, A. Gambaro, R. Piazza, S. Ferrari, A.M. Stortini, I. Moret and G. Capodaglio, PCBs and PAHs in sea surface microlayer and subsurface water samples of the Venice Lagoon (Italy), Mar. Pollut. Bull., 52 (2005) 184-192. 

Rice CP, Meyers PA, Brown GS (1983) Physical behavior of PCBs in the Great Lakes. In Mackay D, Paterson S, Eisenreich SJ, Semmens MS (eds) Role of surface microlayers in the air-water exchange of PCBs. Ann Arbor Science, Ann Arbor, MI p 157... 

Kucklick, J.R. and T.F. Bidleman (1994). Organic contaminants in Winyah Bay, South Carolina. I. pesticides and polycyclic aromatic hydrocarbons in subsurface and microlayer waters. Marine Environ. Res., 37 63-78. 

Abd-Allah, A.M.A., 1999. Organochlorine contaminants in microlayer and subsurface water of Alexandria Coast, Egypt. J. AOAC Int. 82, 391-398. 

Wurl, O., Obbard, J.P., 2006. Distribution of organochlorine compounds in the sea-surface microlayer, water column and sediment samples of Singapore s marine environment. Chemosphere 62, 1105-1115. 

There are very few measurements of the DMS concentration in the sea surface microlayer. The first report (44) indicated an enrichment of 5 times relative to underlying water samples. Other reports indicate that no enrichment was observed in tne microlayer DMS concentration (23.47.511. These differences may be related to the sampling techniques used. It is possible that chemical and biological processes in tne sea surface microlayer may affect the transfer of DMS from the bulk ocean to the atmosphere. However, at present, very little is known about the processes affecting the chemistry of DMS in the microlayer. 

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