Lethal Responses

ERDC TN-DOER-E9

May 2000

The lowest concentration duration dosage that elicited a sublethal response occurred at 650 mg/L

for 5 days exposure, causing elevated hematocrit levels in white perch (Sherk et al. 1974). The

longest duration for which responses to suspended sediments were available for estuarine fish is 14

days, which at a concentration of 1,500 mg/L, caused elevated hematocrit levels in striped bass

(Figure 1).

Lethal Responses. Sherk, O'Connor, and Neumann (1975) and Sherk et al. (1974) used fuller's

earth to generate mortality curves (lethal concentrations that produce 10, 50, and 90 percent

mortality rates (LC10, LC50, LC90)) for six species: white perch, spot (Leiostomus xanthurus),

Atlantic silversides (Menidia menidia), bay anchovies (Anchoa mitchelli), mummichogs (Fundulus

heteroclitus), and striped killifish (F. majalis). Other species were also tested for suspended-

sediment tolerances, but concentration-dependent mortality curves were not determined. Based on

the results of these tests, fish were classified as either tolerant (24 hr LC10 > 10,000 mg/L), sensitive

(LC10 < 10,000 > 1,000 mg/L), or highly sensitive (LC10 <1,000 mg/L) to suspensions of fuller's

earth. The tolerant species were the mummichog, striped killifish, spot, toadfish (Opsanus tau),

hogchoker (Trinectes maculatus), and cusk eel (Rissola marginata), all of which commonly occur

near the substrate-water interface where suspended-sediment concentrations tend to be highest.

White perch, bay anchovy, juvenile menhaden (Brevoortia tyrannus), striped bass, Atlantic croaker,

and weakfish (Cynoscion regalis) were classified as sensitive species. This grouping of fish did not

share a particular habitat preference. Highly sensitive species included Atlantic silversides, juvenile

bluefish (Pomatomus saltatrix), and young-of-the-year white perch.

The accumulated data from studies of estuarine and coastal fish are largely limited to effects of

exposures between 1 and 11 days, at concentrations between 100 and 10,000 mg/L (Figure 1).

Responses are highly species-specific, with lethal effects observed at dosages as low as several

hundred mg/L for 24 hr, or no effect at concentrations above 10,000 mg/L for 7 days. Atlantic

silversides and white perch were among the estuarine fish with the most sensitive lethal responses

to suspended-sediment exposures, exhibiting 10 percent mortality at concentrations less than 1,000

mg/L for 1- and 2-day durations, respectively. The lethal effects of natural muds were tested for

white perch, killifish, and spot, and in general, higher concentrations of natural muds were required

to elicit the same mortality level that occurred when fuller's earth was used for equivalent exposure

durations (Sherk, O'Connor, and Neumann 1975; Sherk et al. 1974).

Estuarine and Coastal Shellfish

Egg and Larval Stages. The effects of suspended sediments on bivalve egg survival have been

investigated for the eastern oyster (Crassostrea virginica) (Davis 1960) and hard clams (Mercenaria

mercenaria) (Davis and Hidu 1969) (Table 2). Although the duration of exposure to various

suspended-sediment concentrations was not given in these studies, it is known that the egg stage

lasts only several hours for oysters (Cake 1983) and about 12 hr for clams (Mulholland 1984). These

investigators measured the percentage of eggs that developed to the straight-hinged larval stage.

Negative impacts to oyster egg development occurred at 188 mg/L of silt, compared with 1,000

mg/L for clam eggs. Larval development continued normally at suspended-sediment concentrations

less than 750 mg/L, whereas higher concentrations for durations of 10 and 12 days consistently had

lethal effects for clams and oysters, respectively.