Environmental Engineering Reference
In-Depth Information
leaching from products treated with arsenic, such as wood. Synthetic organic
arsenic is also used in fertilizer. Arsenic toxicity is primarily associated with
inorganic arsenic ingestion and has been linked to cancerous health effects,
including cancer of the bladder, lungs, skin, kidney, nasal passages, liver,
and prostate. Arsenic ingestion has also been linked to noncancerous car-
diovascular, pulmonary, immunological, and neurological, endocrine prob-
lems. According to USEPA's Safe Drinking Water Act (SDWA) Arsenic Rule,
inorganic arsenic can exert toxic effects after acute (short-term) or chronic
(long-term) exposure. Toxicological data for acute exposure, which is typi-
cally given as an LD
50
value (the dose that would be lethal to 50% of the test
subjects in a given test), suggests that the LD
50
of arsenic ranges from 1 to 4
milligrams arsenic per kilogram (mg/kg) of body weight. This dose would
correspond to a lethal dose range of 70 to 280 mg for 50% of adults weigh-
ing 70 kg. At nonlethal, but high, acute doses, inorganic arsenic can cause
gastroenterological effects, shock, neuritis (continuous pain), and vascular
effects in humans. USEPA has set a maximum contaminant level goal of 0 for
arsenic in drinking water. In 2006, the enforceable maximum contaminant
level (MCL) for arsenic was lowered from 0.050 mg/L to 0.010 mg/L.
The SDWA requires arsenic monitoring for public water systems. The
Arsenic Rule indicates that surface-water systems must collect one sample
annually; groundwater systems must collect one sample in each compliance
period (once every 3 years). Samples are collected at entry points to the dis-
tribution system, and analysis is usually done in the lab using one of sev-
eral USEPA-approved methods, including inductively coupled plasma-mass
spectroscopy (ICP-MS) and several atomic absorption (AA) methods. Several
different technologies, including colorimetric test kits and portable chemical
sensors, are currently available for monitoring inorganic arsenic concentra-
tions in the field. These technologies can provide a quick estimate of arsenic
concentrations in a water sample and may prove useful for spot-checking dif-
ferent parts of a drinking-water system (e.g., reservoirs, isolated areas of dis-
tribution systems) to ensure that the water is not contaminated with arsenic.
Biochemical Oxygen Demand (BOD) Analyzers
One manufacturer has adapted a BOD analyzer to measure oxygen consump-
tion as a surrogate for general toxicity. The critical element in the analyzer is
the bioreactor, which is used to continuously measure the respiration of the
biomass under stable conditions. As the toxicity of the sample increases, the
oxygen consumption in the sample decreases. An alarm can be programmed
to sound if oxygen reaches a minimum concentration (i.e., if the sample is
strongly toxic). The operator must then interpret the results into a measure of
toxicity. Note that, at the current time, it is difficult to directly define the sen-
sitivity or the detection limit of toxicity measurement devices because lim-
ited data are available regarding the specific correlation of decreased oxygen
consumption and increased toxicity of the sample.
