| Land use change results in soil migration into aquatic streams during storm events. This suspended sediment, even in the absence of adsorbed contaminants, may be a significant stressor to aquatic organisms. In some parts of the US, total suspended solids (TSS) concentrations surpass 100,000 mg/L during storm events. The limited data on effects of suspended sediment concentrations on freshwater fishes has mainly focused on salmonids or ecosystem level consequences such as habitat alteration. Few studies have quantified sublethal physiologic effects of suspended solids on water column organisms. This research determined the effects of suspended clay-sized particles on Daphnia magna and Pimephales promelas (Fathead minnow).; D. magna, exposed to natural and defined clay-sized suspensions, had 7-d LC50 values ranging from 5 mg/L to 75 mg/L with montmorillonite being more toxic than kaolinite. Natural clay-sized particles, which were composed of approximately 60% kaolinite, exhibited a 7-d LC 50 value of 51 mg/L, which may indicate a connection between particle source and toxicity. Suspended clay-sized particles rapidly filled the intestinal tract of daphnids ultimately leading to starvation. When transferred to clean media gut clearance occurred within 30 minutes suggesting quick recovery between pulsed exposures.; Fathead minnows were exposed to concentrations ranging from 50 mg/L to 1,000 mg/L of natural and defined clay-sized particles. Whole-body sodium, gill Na+/K+-ATPase activity, and percent body moisture were chosen as endpoints representing the ionoregulatory abilities of the fish. Only montmorillonite produced a statistically significant effect in the form of increased gill Na+/K+-ATPase activity and decreased whole-body sodium concentrations. This effect was seen in the first 12 hours of exposure and is thought to have led to mortality in some organisms exposed to 1,000 mg/L montmorillonite.; This study was an effort to not only investigate sublethal effects of suspended clay-sized particles on aquatic organisms, but also an effort to standardize toxicity testing by exploring relationships between standard and non-standard particle types. The results of such comparisons, in the form of varying LC50 values and differing effects on gill enzyme activity, show that achieving reproducible effects using dissimilar sediment sources is unlikely. However, results of this research underscored the need to treat suspended sediment as a water column contaminant. |
