LIBS in Environmental Sciences

Laser-Induced Breakdown Spectroscopy (LIBS) is an emergent technique that allows an immediate assessment of the elemental composition of materials. It has significant advantages over other conventional analytic methods. Among them the fact that the sample requires no previous preparation and it can have any size and shape. Also, the complexity of the measuring process is considerably reduced. Recently, several reports of LIBS applied to the determination of heavy metals as Pb, Cd, Hg, Cr in food products, vegetables, and fruits were published​

The ability of laser-induced breakdown spectroscopy (LIBS) to interrogate solid samples has been demonstrated for the direct analysis of plant materials (e.g. leaves, roots, and fruits) in the widespread scenario of agricultural and environmental sciences. In general, test sample presentation varies from fresh or dried materials (e.g. whole leaf, leaf section, whole grain, and vegetables) to pellets prepared from the ground and/or comminuted materials.

Example:

 

Nile Tilapia is a teleost fish native from Africa, belonging to the Cichlidae family, inhabits most of the tropical regions where conditions are favorable for reproduction and growth. Its cultivation began in 1820 in Africa and from there spread to the rest of the world.  This fish withstand adverse environmental conditions, tolerates low oxygen concentrations, and can be grown in ponds and cages. For these reasons, the consumption of Tilapia has extended worldwide. Since it is one of the most accepted species in world aquiculture it is a fact that the natural habitat of the Nile Tilapia is being polluted by the increasingly intense development of industrial-technological processes which release untreated toxic waste onto seas, rivers, lakes, and also in artificial harvesting pools. This increases the chances of encountering heavy metals like copper and lead as contaminants in this fish.

Considering their biological function, heavy metals are classified as essential for life, as is the case of Fe, Cu, Zn, and Sn, and non-essential, like Hg, Pb, and Cd. The latter are considered toxic to the organism in any level of concentration, although there are maximum permissible levels, regulated by international standards.  Meanwhile, Cu and Pb are bio-accumulative elements in plant and animal species, which presence is particularly serious for the Nile Tilapia, since it is located very low in the natural trophic chain, due to its diet based on algae, decomposing matter, and plankton. On the other hand, it should be noted that in most cases, high concentrations of chemical substances don´t change the appearance of food; therefore the contamination is not apparent to the eye and will go unnoticed.

Due to the dangerous effects of heavy metals on human health, there is a need for fast and portable analytical techniques for food control. Edible fish also requires techniques for controlling in situ the presence of these contaminants when they are above the levels allowed by international standards. 

 We show a new laser-induced breakdown spectroscopy (LIBS) setup based on a small, ultracompact, and low-cost excitation source developed by the authors. The laser is a compact Nd:YAG laser emitting in the multipulse 𝑄Q-switch regime and is capable of delivering a bunch of pulses with a total energy of up to 300 mJ. The developed system is applied to the analysis of Pb and Cu contaminants on fish. LIBS spectra were obtained from scales, muscle, and skin of fresh and frozen samples. The developed excitation source is able to detect 0.25 mg/Kg and 0.20 mg/Kg of Pb and Cu, respectively. In this way, the equipment seems to be adequate to achieve a screening analysis of those contaminants.

(https://doi.org/10.1364/AO.54.004453)

Relative Concentration of Cu and Pb Measured by LIBS and Atomic Absorption Spectroscopy

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LIBS spectra of lead and copper on scale (a) and (b) and skin (c) and (d)

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LIBS spectra were taken from the muscle of frozen (a) and fresh (b) fish.