text: Toxic metals can be present in the aqueous environment at trace or ultra-trace concentrations, yet still be toxicologically significant and thus cause harm to humans or the environment. Because these concentrations are so low, they would fall beyond the detection limits of most analytical instruments if the media had been sampled using traditional grab samples. Using SLMDs to passively collect metals over an extended period of time allows for trace metals to accumulate to detectable levels, which can give more accurate estimate of aquatic chemistry and contamination. SLMDs also have the advantage of being able to capture pulses of metal contamination that might otherwise go undetected when using grab samples.
  SLMDs are limited to the assessment of labile metals, and cannot be used to monitor for organic contaminants. Further, while the ability of SLMDs to sample copper, zinc, nickel, lead, and cadmium has been repeatedly demonstrated, there has been little laboratory research on their ability to reliably uptake other toxic metals. Still, while laboratory studies on the effectiveness of SLMDs have only investigated copper, zinc, nickel, lead, and cadmium, SLMDs have been used with success in field studies to assess a wider range of metals.