There is some evidence to suggest that the MCL should be lowered but the EPA and World Health Organization continue to use 0.01 mg/L (10 ug/L) as the maximum allowable amount of arsenic [3]. This has less to do with the known exposure levels at which negative health impacts occur but rather the technological limit of measuring and purification technology. In fact, the EPA has a non-enforceable Maximum Contaminant Level Goal of 0 ug/L and they proposed a MCL of 5 ug/L (0.005 mg/L) for a national standard but this was never adopted [3].

Because arsenic is a naturally occurring element, it is also found in the waters of the Chesapeake Bay. The concentrations of this compound have less to do with human activity and more to do with river flow (which is connected to how much groundwater is entering the system) and with biological processes that cycle arsenic through different forms. During hypoxic periods (recall from last month that this means low oxygen levels in the water), inorganic forms of arsenic are released from sediments at the bottom of the Bay, while phytoplankton produce organic forms of arsenic when phosphorus is a limiting nutrient [4]. And while some arsenic is naturally occurring, some does come from humans in the form of urban runoff but also through the use of arsenic based wood treatments like Chromated Copper Arsenate, which is commonly used for pilings and bulkheads. However, arsenic is not generally considered a problem contaminant in the Chesapeake Bay, except from certain types of pollution such as coal ash [5]. This means that there is no specific target for arsenic levels in the Chesapeake Bay and researchers do not sample for it as part of routine environmental water quality analysis.