AMD Pollutants:  Heavy Metals and pH

Water riddled with AMD typically has high concentrations of heavy metals and H+ ions, which causes the pH to decrease dramatically and take on an orange hue as the metals react to form iron oxide and hydroxide precipitates.  These precipitates, called ocher, form a coating along the bottom of river and stream beds. 

Effects on Human Health

For people's health to be affected by acid mine drainage, people have to be exposed to the pollutants either from the water or the contaminated organisms that live in or around it.  To date, there is a minuscule amount of data that shows how much humans are affected by AMD.  However, there is a substantial amount of information on many of the components and pollutants in AMD that are hazardous.

Heavy metals have detrimental side effects on human health due to their acute long-term toxicity.  These metals, once present, are difficult to remove.  Therefore, they can remain in natural ecosystems for extended periods of time.  Additionally, when these metals are ingested, they are capable of wreaking havoc on the body.  The metals accumulate in different systems that disrupt metabolic functions. As these metabolic processes are disrupted organs’ vital functions are impaired, and nutritional minerals are moved from their desired locations.   A list of some heavy metals with their side effects is outlined below 

The ochre produced by lowered pH, kills off many of the macroinvertebrates that feed along the riverbed which fish feed upon. Thus, ochre causes the extended food chain to be disrupted, not only for humans but the ecosystems surrounding the contaminated site as well.  

Effects on Aquatic Life

Fish, in particular, can be severely affected by AMD.  Fish populations can be exposed directly to heavy metals and H+ ions through their gills and causes acute toxicity that impairs their respiration.   The H+ ions (pH) alter their gill membranes or the mucus around them and causes hypoxia, ultimately leading to death. The ochre that coats the streambeds destroys habitat makes it difficult for fish to find clean gravel to use for spawning and decreases the food supply.  Additionally, when the pH of the contaminated water reaches levels as low as 2-4.5,it leads to the extinction of most aquatic organisms, not just fish.  Many fish populations can survive in contaminated waters with pHs as low as 5, but once pH levels hit 4.5 90% of the fish population is exterminated.

If the fish are not killed directly by the heavy metal toxins and H+, then they may suffer from nonlethal abnormalities like stunted growth, reduced reproduction, deformities, and lesions.  

Effects on Plant Life

Plants are directly dependent on balanced pH for macro and micronutrients from the soil.  Keep elements for successful plant growth are tied up in the ground when the pH is acidic (~pH 1-4) like calcium, nitrogen, and phosphorous. The microorganisms that decompose organic matter are relatively sedentary at these pH levels thus impeding the better use of nutrients, root development, and drought tolerance.   Very few plant species can survive at such highly acidic concentrations; it’s limited almost exclusively to types of algae and mosses.  Heavy metals or certain combinations of heavy metals can lead to cellular damage and disrupt critical processes needed for plant growth.  Some side effects include reduced chlorophyll production, seed germination, protein, chlorophyll and enzymes production.