Distribution,sources and risk of exposure to polycyclic aromatic hydrocarbons in indoor dusts from electronic repair workshops in southern Nigeria

This study evaluates the characteristic levels,sources and risk of human exposure to polycyclic aromatic hydrocarbons(PAHs)in indoor dusts from electronic repair workshops in southern Nigeria.The dust samples were collected by gentle sweeping with a brush and dustpan,and subsequently dried and extracted with hexane/dichloromethane by ultrasonication.The extracts were purified on a silica gel/alumina column,and then analysed for their PAH content by means of gas chromatography-mass spectrometry.The concentrations of PAHs in the electronic repair workshop dusts ranged between 205 and 2963 mg kg
1.The compositional patterns indicate the dominance of 5-and 3-ring PAH homologues.The estimated benzo[a]pyrene carcinogenic(BaPTEQ)and mutagenic(BaPMEQ)potency concentrations ranged from 67 to 401 mg kg^-1 and 56.5e277 mg kg^-1 respectively.The non-cancer risk(hazard index,HI)arising from human contact with PAHs in the electronic repair workshop dusts were less than one for all human subject age groups indicating that there is no considerable non-cancer risk.The cancer risk values for the ingestion and dermal contact routes were greater than the acceptable risk of 10^-6,which suggests that there is a considerable cancer risk associated with unconscious ingestion and dermal contact with dust particles from these electronic repair workshops.The isomeric ratios for the PAHs in the dust samples and principal component analysis suggest that combustion of biomass and vehicular emissions were responsible for the presence of PAHs in the electronic repair workshop dusts.

Laser Erasing and Rewriting of Flexible Copper Circuits

Integrating construction and reconstruction of highly conductive structures into one process is of great interest in developing and manufacturing of electronics,but it is quite challenging because these two involve contradictive additive and subtractive processes.In this work,we report an all-laser mask-less processing technology that integrates manufacturing,modifying,and restoring of highly conductive Cu structures.By traveling a focused laser,the Cu patterns can be fabricated on the flexible substrate,while these as-written patterns can be selectively erased by changing the laser to a defocused state.Subsequently,the fresh patterns with identical conductivity and stability can be rewritten by repeating the writing step.Further,this erasing–rewriting process is also capable of repairing failure patterns,such as oxidation and cracking.Owing to the high controllability of this writing–erasing–rewriting process and its excellent reproducibility for conductive structures,it opens a new avenue for rapid healing and prototyping of electronics.