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Published: March 24, 2011
r 2011 American Chemical Society 3539 dx.doi.org/10.1021/es102790d | Environ. Sci. Technol. 2011, 45, 3539–3546
ARTICLE
pubs.acs.org/est
Enumerating Sparse Organisms in Ships’ Ballast Water: Why Counting
to 10 Is Not So Easy
A. Whitman Miller,*,† Melanie Frazier,‡ George E. Smith,† Elgin S. Perry,§ Gregory M. Ruiz,† and
Mario N. Tamburri^
†Smithsonian Environmental Research Center, PO Box 28, Edgewater, Maryland 21037, United States
‡Western Ecology Division, National Health and Environmental Effects Research Laboratory, O ffice of Research and Development, U.S.
Environmental Protection Agency, 2111 SE Marine Science Drive, Newport, Oregon 97365, United States
§Statistics Consultant, 2000 Kings Landing Road, Huntingtown, Maryland 20639, United States
^Maritime Environmental Resource Center, Chesapeake Biological Laboratory, University of Maryland Center for Environmental
Science, One Williams Street, Solomons, Maryland 20688, United States
bS Supporting Information
’ INTRODUCTION
Maritime transportation is a foundation of the global market.
There are well over 50,000 commercial ships which move goods
around the world among over 300 major ports.1,2 However, the
ballast water associated with merchant vessel traffic is also
responsible for the transfer and introduction of aquatic invasive
species to coastal waters where they can cause enormous
ecological and economic damage.3 5
In an attempt to minimize the risk of BW introductions, the
International Maritime Organization (IMO6) and U.S. Coast
Guard (USCG7) have each proposed discharge standards limit-
ing maximum concentrations of living organisms that can be
released with BW, including new regulations requiring ship
operators to meet those limits. The USCG has proposed to
implement regulations in two phases: phase 1 proposes to set
standards similar to current IMO standards and phase 2 proposes
standards up to 1,000 times stricter. The IMO and USCG phase
1 standards require BW discharged by ships to contain:
1 Fewer than 10 viable organisms 3 m 3 g50 μm in minimum
dimension or smallest measure among length, width, and
height excluding fine appendages such as sensory antenna
and setae (the majority of organisms in this size class are
zooplankton).
2 Fewer than 10 viable organisms 3 mL 1 <50 μm and g10
μ m in minimum dimension. (The majority of organisms in
this size class are protozoa, including zooplankton).
3 Fewer than the following concentrations of indicator mi-
crobes, as a human health standard: (a) toxicogenic Vibrio
cholerae (serotypes O1 and O139) with <1 colony forming
unit 3 100 mL 1 ; (b) Escherichia coli <250 cfu 3 100 mL 1;
and (c) intestinal Enterococci <100 cfu 3 100 mL 1 .
To achieve the above discharge standards, technology devel-
opers and manufacturers around the world are advancing on-
board BW treatment systems8,9 that use methods such as filtration þ
UV radiation, deoxygenation, ozonation, and chlorination.9
Received: August 14, 2010
Accepted: March 8, 2011
Revised: February 14, 2011
ABSTRACT: To reduce ballast water-borne aquatic invasions worldwide, the International
Maritime Organization and United States Coast Guard have each proposed discharge
standards specifying maximum concentrations of living biota that may be released in ships’
ballast water (BW), but these regulations still lack guidance for standardized type approval
and compliance testing of treatment systems. Verifying whether BW meets a discharge
standard poses significant challenges. Properly treated BW will contain extremely sparse
numbers of live organisms, and robust estimates of rare events require extensive sampling
efforts. A balance of analytical rigor and practicality is essential to determine the volume of
BW that can be reasonably sampled and processed, yet yield accurate live counts. We
applied statistical modeling to a range of sample volumes, plankton concentrations, and
regulatory scenarios (i.e., levels of type I and type II errors), and calculated the statistical
power of each combination to detect noncompliant discharge concentrations. The model
expressly addresses the roles of sampling error, BW volume, and burden of proof on the
detection of noncompliant discharges in order to establish a rigorous lower limit of
sampling volume. The potential effects of recovery errors (i.e., incomplete recovery and
detection of live biota) in relation to sample volume are also discussed.