Ref. No. [UMCES]CBL 2013-021
ACT VS12-05
EXECUTIVE SUMMARY
Instrument performance verification is necessary so that effective existing technologies can
be recognized, and so that promising new technologies become available to support coastal science,
resource management, and ocean observing systems. The Alliance for Coastal Technologies (ACT)
has therefore completed an evaluation of commercially available in situ hydrocarbon sensors. This
verification included test applications for: (1) controlled laboratory tanks with additions of various
organic, fluorescent compounds, (2) experimental wave tank with additions of two sources of crude
oils with and without dispersants, (3) a moored deployment in Baltimore Harbor, and (4) hydrocast
surveys in the Gulf of Mexico at a site near a submerged leaking oil barge. In this Verification
Statement, we present the performance results of the WETLabs ECO FLCDRTD (CDOM)
fluorometer. Quality assurance (QA) oversight of the verification was provided by an ACT QA
specialist, who conducted technical systems audits and a data quality audit of the test data.
Response specificity of the ECO FLCDRTD fluorometer to a range of organic compounds
was evaluated in a series of lab tests. The instrument output was based on a linear response
photodetector behind the emission optical filters with response output provided in raw counts.
Instrument response with respect to challenge compound concentration varied with respect to the
inherent fluorescence properties of the challenge compound as well as sensor optics. As expected,
the FLCDRTD
exhibited concentration dependent linear responses to several of the challenge
compounds with response sensitivity ranked as quinine sulfate >> carbazole > naphthalene disulfonic
acid and was insensitive to basic blue. Instrument failure, after shipping between sites, precluded
assessment of sensitivity to #2 Diesel Fuel challenges. Trials in the COOGER wave test tank at the
Bedford Institute of Oceanography revealed linear responses from 0.3 to 12 ppm total added crude
oil in the presence of chemical dispersant. For trials where no chemical dispersant was added, the
instrument response decreased slightly as oil concentrations were increased above 1.5 ppm. A
greater presence of oil was noted on all downward oriented surfaces of the instruments and
deployment frame after non chemically-dispersed trials, so likely this response was due to oil
accumulation on the optical surfaces. Daily initial baseline signals changed with ambient water
quality conditions. Instrument responses to various challenge compounds converged when compared
to standardized EEMs fluorescence intensity estimated to correspond to the instruments emission
optics.
Field deployments in Baltimore Harbor and northern Gulf of Mexico were equivocal as all
field reference samples were close to or below the reporting (50 ppb) or limit of detection for total
petroleum hydrocarbons (25 ppb) for the reference analytical method. However, for Baltimore
Harbor the FLCDRTD output was substantially higher than the baseline response in deionized water
(50-100 counts) and was correlated with environmental background fluorescence as determined by
EEMs analysis. There was no clear instrument response to EEMs intensities in the Gulf of Mexico
profiling test. It is unclear if the response may have been impacted by the use of a second party data
logger for this profiling application.
During this evaluation, no problems were encountered with the provided software, set-up
functions, or data extraction at any of the test sites. Operator error impacted one hydrocast profile
and excessive instrument noise was encountered in the final laboratory trial of #2 Diesel Fuel which
was conducted after all other field deployments. In general, results indicate that for all types of test
applications including lab, moored and hydrocast surveys, the ambient fluorescence properties of the
challenge solution need to be accounted for to make quantitative hydrocarbon estimates from these
sensors. We encourage readers to review the entire document for a comprehensive understanding of
instrument performance.
