In‐situ enrichment of heavy metals from deep‐sea water by an ion‐exchange pump system

Abstract

A deep‐sea pump system, originally designed as an in‐situ particle sampler, was modified into an “in‐situ heavy‐metal sampler” in order to overcome the problems of shipboard contamination and low concentration in seawater analysis. The pump system was equipped with a prefilter, ion‐exchange columns, and an inductive flow meter to measure low flow rates. Preconcentration factors of up to 500 could be achieved in a pumping time of about 5 h. Metal analysis was done onboard ship by measuring the enriched solutions with stripping voltammetric methods. The pumping device was tested and optimized on four research cruises under varying conditions. Data from the Mediterranean Sea and the northeast Atlantic for up to eight heavy metals, including Mn, Fe, Co, Ni, Zn, Cu, Cd, and Pb, suggest the wide applicability of the system and the advantage of the in‐situ preconcentration process.

Though the first pumping system was optimized on several cruises, constructive faults in principle had not been overcome. A completely new system with a precisely adjustable peristaltic pump and a programmable electronic microcontroller unit was developed. Two prototypes of the new system were tested successfully during R.V. Sonne cruise SO 92 in the Indian Ocean. The deployment of the “in‐situ heavy‐metal sampler” allowed the measurement of heavy‐metal concentrations in normal seawa‐ter and the detection of anomalies due to natural and anthropogenic sources.

Keywords:

• Bannock Basin
• deep‐sea pump
• heavy‐metal analysis
• in‐situ enrichment
• ion exchange
• Mediterranean Sea microcontroller
• event‐controlled sampling
• Northeast Atlantic
• stripping voltammetry