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G.E. Napolitano and D.S. Cicerone
microtome for further analysis of sections of the desired thickness. Due to the
speed of sampling (the surface microlayer is frozen in < 1 s), this technique is
particularly useful under rough water conditions.
Another unconventional sampling device designed to measure chemicals at the
air-water interface consists of a prism of optically polished germanium (Baier,
1970). Surface films are captured by a simple dip mechanism of the prism into the
water. The polar head groups of the organic material are adsorbed onto the
hydrophilic surface of the prism, obtaining a thin (0.01 /-Lm) film of the microlayer.
The simplest device to sample the water microlayer is probably the glass plate.
A small (~0.20 x 0.20 m) glass plate can be applied and then withdrawn vertically from the water surface by manual motion at a rate of 0.20 m . s - I and
wiped off with a windshield wiper blade (Harvey and Burzell, 1972). This device
samples the top 60-100 /-Lm of the water surface (Table 10.3). According to Hardy
et al. (1988), the glass plate has collection characteristics that are similar to those
of the PTFE-coated rotating devices. However, the former requires a considerably
larger effort to obtain an acceptable sample size. In a variation of the glass plate
technique, Larsson et al. (1974) used a perforated PTFE plate to collect lipids
from the water-surface microlayer along the Swedish west coast. Although a
quantitative assessment of the efficiency of this type of plate is not reported, the
authors postulate that the recovery of lipids from the water microlayer can be
augmented by the use of a densely perforated PTFE surface.
In another attempt to modify the simple glass plate method, Gever et al. (1996)
used a silanized borosilicate glass plate to sample the surface microlayer of a rice
field. The plates (silanized with 5% solution of dichlorodimethylsylane) are used
in a way similar to conventional glass plates in that the hydrophobic materials in
the microlayer are extracted by running an organic solvent from a Pasteur pipette
across the plate.
This brief assessment of the different instruments and methods used in sampling the surface micro layer demonstrates the wide spectrum of available materials and designs. Because each technique has its own advantages and drawbacks,
the optimal method cannot be recommended without taking into consideration the
type of environment, the prevailing flow conditions, and the size of sample
needed. In general, the most important characteristics to consider in evaluating a
particular sampling equipment are the inertness and hydrophobicity of the materials, speed of operation, low potential for introducing contaminants from the craft
and the support equipment, and consistency in the thickness of the film sampled.
Due to inertness and versatility considerations, PTFE screens, surfaces, and accessories (wipers and collecting cups) are highly recommended for the sampling
of biogenic lipids and hydrophobic contaminants from surface waters. A PTFE
screening material (~360-500-/-Lm mesh) and PTFE sheets are recommended by
the American Society for Testing Materials (1995) to sample oil spills and slicks
from surface waters. Unfortunately, we are not aware of any environmental or
ecological study that has used or tested this supposedly standard technique. Furthermore, authoritative and widely used handbooks of water analysis do not
G.E. Napolitano and D.S. Cicerone
microtome for further analysis of sections of the desired thickness. Due to the
speed of sampling (the surface microlayer is frozen in < 1 s), this technique is
particularly useful under rough water conditions.
Another unconventional sampling device designed to measure chemicals at the
air-water interface consists of a prism of optically polished germanium (Baier,
1970). Surface films are captured by a simple dip mechanism of the prism into the
water. The polar head groups of the organic material are adsorbed onto the
hydrophilic surface of the prism, obtaining a thin (0.01 /-Lm) film of the microlayer.
The simplest device to sample the water microlayer is probably the glass plate.
A small (~0.20 x 0.20 m) glass plate can be applied and then withdrawn vertically from the water surface by manual motion at a rate of 0.20 m . s - I and
wiped off with a windshield wiper blade (Harvey and Burzell, 1972). This device
samples the top 60-100 /-Lm of the water surface (Table 10.3). According to Hardy
et al. (1988), the glass plate has collection characteristics that are similar to those
of the PTFE-coated rotating devices. However, the former requires a considerably
larger effort to obtain an acceptable sample size. In a variation of the glass plate
technique, Larsson et al. (1974) used a perforated PTFE plate to collect lipids
from the water-surface microlayer along the Swedish west coast. Although a
quantitative assessment of the efficiency of this type of plate is not reported, the
authors postulate that the recovery of lipids from the water microlayer can be
augmented by the use of a densely perforated PTFE surface.
In another attempt to modify the simple glass plate method, Gever et al. (1996)
used a silanized borosilicate glass plate to sample the surface microlayer of a rice
field. The plates (silanized with 5% solution of dichlorodimethylsylane) are used
in a way similar to conventional glass plates in that the hydrophobic materials in
the microlayer are extracted by running an organic solvent from a Pasteur pipette
across the plate.
This brief assessment of the different instruments and methods used in sampling the surface micro layer demonstrates the wide spectrum of available materials and designs. Because each technique has its own advantages and drawbacks,
the optimal method cannot be recommended without taking into consideration the
type of environment, the prevailing flow conditions, and the size of sample
needed. In general, the most important characteristics to consider in evaluating a
particular sampling equipment are the inertness and hydrophobicity of the materials, speed of operation, low potential for introducing contaminants from the craft
and the support equipment, and consistency in the thickness of the film sampled.
Due to inertness and versatility considerations, PTFE screens, surfaces, and accessories (wipers and collecting cups) are highly recommended for the sampling
of biogenic lipids and hydrophobic contaminants from surface waters. A PTFE
screening material (~360-500-/-Lm mesh) and PTFE sheets are recommended by
the American Society for Testing Materials (1995) to sample oil spills and slicks
from surface waters. Unfortunately, we are not aware of any environmental or
ecological study that has used or tested this supposedly standard technique. Furthermore, authoritative and widely used handbooks of water analysis do not