Extraction of lead, zinc and copper in seaweed using pressurized hot water and acid digestion

Abstract

Introduction: This study was performed to optimize extraction of lead, copper and zinc from seaweed using pressurized hot water, to investigate the selectivity and extractability of the extraction.

Background: Pressurized hot water extraction is an environmentally sustainable method in comparison to more common extraction methods, such as distillation or solvent extraction, used with plant material. Extraction of metals in seaweed using pressurized hot water is unusual and information about this is limited.

Aim: The aim of this study is to find the extraction variables where selective extractions (where the extraction for one metal is efficient but the other metals are inefficient) for all the metals are performed and where high extractability is reached.

Methods: The pressurized hot water extraction is performed at varying temperatures, between 60-180 °C, with and without additives, such as formic acid and different extraction times, between 1 to 9 static cycles with 10 minutes on each cycle. The extractions will then be analysed using atomic absorption spectroscopy, the measured absorbances will be compared to a concentration curve made from standards with known concentrations.

Results: All the measurements of lead were negative. The extractions were contaminated by copper and zinc, influencing the measurements. The highest amount of zinc was extracted using 180 oC, with addition of 2,5 % formic acid and 9 extraction cycles.

Conclusion: There were no lead found in the extract, therefor nothing can be said about the extractability or the selectivity of the extraction of lead. Due to contamination no conclusions can be formed about the extractability or selectivity of copper. An increase of temperature positively influenced the extraction of zinc, addition of formic acid also positively influenced the extraction. The extraction time did not influence the extraction of zinc as much as the other two experimental variables, but it had a slight positive influence.

Popular Abstract

Why should you eat seaweed? Previous research has suggested it is good for both health and environment. Even so it is important to know that seaweed is good at absorbing toxic substances that may be harmful if we ingest too much of them. To prevent sickness, we need to know if the seaweeds contain the toxic substances. In this report seaweeds from Norway are analysed to see if they have high amounts of metals such as lead, zinc and copper, making them toxic. Lead is a toxic metal while copper and zinc are essential but can be harmful if too much is ingested.
The metals need to be extracted and then analysed. And it is important to optimize extraction methods of the toxic metals and other substances. The extraction will be performed using different experimental variables. It can be difficult to extract the wanted metals, but other minerals and healthy polyphenols (antioxidants) may easily be extracted, therefor removing heathy substances and not the harmful ones. The optimization is needed to increase the selectivity of the extraction.
Extraction methods usually require large volumes of toxic solvents and/or solvents that are bad for the environment. However, pressurized hot water is not toxic and we have plenty of it making it an environmentally sustainable option. To get an accurate picture of how much metal the seaweed contains the extraction also needs to be optimized to retrieve as much of the metals as possible. This was done by changing different variables of the extraction.
The experiment was designed to perform 16 extractions using different combinations of the extraction variables. The temperature was set to go from 60 oC to 120 oC and at the highest 180 oC, the extraction time was 10, 50 and 90 minutes. The solvent was water mixed with acid, and extractions were performed with 2,5% and 5% formic acid as well as with only water.
No lead was detected after extraction using pressurized hot water. Copper was not successfully extracted; the samples were contaminated. The most zinc was extracted at 180 oC, with addition of 2,5 % formic acid and 90 minutes extraction time. The extraction of zinc is more efficient at higher temperatures and with addition of acid. The extraction time did not influence the extraction as much as the other two experimental variables. A nutritional value of the seaweed could not be determined.

• author: Gustafsson, Vendela
• supervisor: Charlotta Turner
• organization: Department of Chemistry
• alternative title: Environmentally sustainable method to extract toxic metals from seaweed
• course: KEML10 20211
• year: 2021
• type: M2 - Bachelor Degree
• subject: Chemistry
• keywords: Atomic Absorption Spectroscopy, Pressurized hot water extraction, Seaweed, Toxic metals, Analytical Chemistry
• language: English
• id: 9057918
• date added to LUP: 2021-07-01 09:04:29
• date last changed: 2021-07-01 09:04:29