In principle, the answer is yes but in practice the effects are very small in most applications because the concentration of dissolved, NIR-absorbing matter is very low in the environment. Absorption of light by materials dissolved in a sample affects the value of turbidity and SSC indicated by an OBS sensor because absorption reduces the light energy available to be scattered by particles as well as the intensity of scattered light that escapes from the sample. Other things being equal, absorption by dissolved matter results in lower scattered light intensity and lower indicated SSC for an absorbing samples than for non-absorbing one.

We conducted tests with dissolved organic and inorganic materials to identify the threshold conditions where OBS function is substantially impaired. We define substantial as a 10% reduction in indicated turbidity. OBS sensors operate in the NIR band so they are colorblind. That is color perceived by an operator has no direct influence on OBS function, however, color can indicate the presence of materials that are strongly absorbing in the operating spectrum. Our inorganic absorber was a blue, Copper +2 dye with an absorptivity, ε, of 23 cm^-1 M^-1 and the organic dye was a brown, haemin-based compound with an ε = 1450 cm^-1 M^-1; see photographs. The absorptivity indicate that a one-molar solutions of the compound will have absorption coefficients of 23 and 1450 cm^-1 (recall that pure water has an absorption coefficient of 0.06 cm^-1 at 875 nm). It therefore takes a miniscule concentration of these materials, less than 100 µM l^-1, to strongly affect sample absorbance and SSC. This is illustrated on the graph, which shows the decline of OBS response to silt-size clear-plastic sphere with increasing dye concentration.