EPA's Vessel General Permit and Small Vessel General

mg/L (USEPA 2008). Average phosphorous concentrations were above EPAs screening level
benchmark of 0.1 mg/L in bilgewater, graywater, deck washdown discharges, fish hold effluent,
and fish hold cleaning effluent. EPA suggested that the likely source of phosphorous in
bilgewater and deck washdown water was liquid detergents used on board for deck washing.
They also indicated that sources of phosphorous in graywater and fish hold effluent may reflect
food or other wastes. Table 29 (3-14 from the BE) shows the average concentrations of
ammonia nitrogen and total phosphorous in the various vessel discharges requiring detailed
analysis.
Table 29. Average Nutrient Concentrations in Vessel Discharges at Levels Above
Screening Level Benchmarks
Vessel Discharge Requiring Detailed
Analysis
Average Ammonia Nitrogen
(mg/L)
Average Total Phosphorous
(mg/L)
Deck Washdown NA 1.7
Fish Hold Effluent 12 13
Fish Hold Cleaning Effluent 16 8.5
Graywater 1.3 1.4
2.1a 10a
Stern Tube Packing Gland Effluent NA 0.13
Source: USEPA, 2010, unless otherwise specified.
NA: Pollutant does not exceed the screening level benchmark for this vessel discharge (see Appendix D of the BE for more
information regarding screening level benchmarks).
a) Average concentration in graywater from large cruise ships (USEPA, 2008, EPA sampling data).
Direct effects of Ammonia Nitrogen
As mentioned above, nitrogen is essential for primary production in aquatic ecosystems and
over-enrichment can lead to eutrophication and water quality impairments. Ammonia nitrogen
(NH3 and NH4-) can also be highly toxic. Recent studies have shown that freshwater mollusks
(mussels and snails) are particularly sensitive to ammonia (Wang et al. 2007a, Wang et al.
2007b, Besser et al. 2009). In fact, they are more sensitive than previously tested species. As a
result, EPA is revising their 304a aquatic life criteria for ammonia to include these new mollusk
data so that freshwater mussels, snails and other mollusks are adequately protected. A draft of
the updated ammonia criteria document was published in the federal register for public comment
in 2009.
EPA used the freshwater mussel Lampsilis siliquoidea (Fatmucket) as a surrogate to represent
freshwater invertebrates in their response analysis. The IC20 for Fatmucket (0.3027 mg N/L)
was the lowest chronic effects thresholds (CTET) among all taxa (freshwater or marine)
considered in the analysis (EPA BE Table 5-49). EPA predicted the concentrations of ammonia
nitrogen in river and estuarine harbors, resulting from vessel discharges, to be 0.0000285 (mg
N/L) and 0.00742 (mg N/L), respectively. These concentrations are orders of magnitude below
the Fatmucket IC20 and the resulting risk quotients were extremely low (EPA BE Table 5-50).
Therefore risks from chronic exposure to ammonia nitrogen in harbors where, vessel discharges
are the sole source, should be very low.
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