Trends in Toxic Metal Levels in Discarded Laptop Printed Circuit Boards

Abstract

Waste printed circuit boards (PCBs) contain toxic metals at concentrations that could pose human and environmental threats if improperly disposed of. Also, PCBs are known to contain appreciable quantities of precious metals with economic value. This study investigated the levels of Cu, Pb, Ni, Zn and Cd in the PCBs extracted from ten discarded laptops and outlined the trends that can be drawn from the results. The laptops were made by a world-wide leading original equipment manufacturer (OEM). The whole laptops were disassembled to enable the extraction of populated PCBs; components were dismounted and all de-populated PCBs were separately crushed, sieved, and total recoverable metals aforementioned were extracted using EPA 3050B method. Also, PCBs were analysed following the EPA Toxicity Characteristic Leaching Procedure (TCLP) and the EPA Synthetic Precipitation Leaching Procedure (SPLP) tests to study their leachability when exposed to municipal landfill and rain water, respectively. The extracts were analysed for metal levels using atomic absorption spectrophotometric technique. The sequence of total recoverable metals was Cu (3.23±0.41%) > Pb (1.95±0.57%) > Ni (0.88±0.36%) > Zn (0.012±0.003%) > Cd (4.00±2.30 mg/kg). Our study revealed a reduction in average % Cu and Zn by at least 6 and 1.5 times, respectively compared with previous studies. The level of Pb also was noticed to decrease from 2.5% in PCBs produced in 2006 to 1.7% in those produced in 2009. On the one hand, this could be a sign of the efforts conducted by OEMs to shift towards the design of eco-friendly products. On the other hand, average Pb (mg/L) level in TCLP and SPLP leachates was respectively 13 and 11 times higher than EPA limit of 5mg/L. Discarded laptop PCBs should still be handled and disposed of as hazardous waste.