For widespread use of biochar in agriculture and horticulture, it must be ensured that application will neither adversely affect soil and plants, nor exceed legislated contaminant concentrations. The most relevant groups of contaminants in biochar are potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOC). In this thesis, the concentrations of these groups of contaminants were analysed in 90 different biochars produced by slow pyrolysis. Subsequently, the concentrations were compared to legislation/guideline threshold values and linked to production conditions. The risk these contaminants pose to plant growth was also assessed, to give recommendations on production of safe biochar. PTEs can neither be formed nor destroyed, which means their presence in biochar is predominantly determined by feedstock type. However, significant levels of Cr, Fe and Ni were introduced into biochar from the furnace steel, whilst PTEs with low boiling points, such as As, Cd and Zn, partially evaporated during pyrolysis. PTEs were not responsible for phytotoxic effects observed for PTE-rich biochars despite biochar’s exceedance of available and total PTE threshold values for soil and soil amendments. Although initial tests were promising, the risk that PTE-rich biochars as amendment for soil and growing media pose, needs further investigation. The PAH concentration in biochar was markedly reduced by increasing carrier gas flow rate, and the type of feedstock also influenced the PAH content. However, there was no clear dependence of pyrolysis temperature on PAH concentrations, which was attributed to PAHs being increasingly formed and evaporated at higher pyrolysis temperatures. Ultimately, condensation of pyrolysis vapours and deposition on biochar was identified as the main risk for biochar contamination with PAHs, as this resulted in elevated concentrations of high-risk, higher molecular weight PAHs. Weaknesses in the pyrolysis unit design, such as cold zones, resulted in elevated concentrations of VOCs, as well as PAHs, in biochar. Comparing concentrations and phytotoxic potential of both compound groups, it was concluded that observed toxic effects were much more likely caused by VOCs in biochars containing both contaminants. Overall, formation of VOCs and PAHs cannot be prevented, but their presence in biochar resulting from retention and deposition can be minimised.

Greenhouse food production has intensive fertilizer practices, and it leads to contamination in the soil and food chains. This study investigated the potentially toxic elements (As, Pb, Zn, Cd, Cr, Cu, and Ni) (PTE) in agriculture soil and their bioaccumulation by dragon fruit and banana. Different fertility tests are conducted to see if there is a correlation between PTEs and fertilizers. CHNS/O analyzer was used to determine organic carbon and nitrogen concentration in the soil. Besides, organic and inorganic phosphorus amounts were analyzed to detect the amount of fertilizer input. Elemental analysis was conducted with ICP-MS. The amount of N, P, and K and PTEs compared and discussed to source the PTEs. Excessive fertilizer practices were acquired, and possible reasons and results were discussed. Besides, the investigations have revealed that concentrations of potentially toxic elements in greenhouse and open-field farms in Gazipaşa/Turkey are below the environmental standards in the soil and fruit samples. Organic farming practices are more dominant than inorganic farming practices in the sampling stations. / Seralarda yapılan gıda üretimi yoğun gübre uygulamalarına sahip olup hem toprakta hem de besin zincirlerinde kontaminasyona yol açmaktadır. Bu çalışma, tarım toprağındaki potansiyel olarak toksik elementleri (As, Pb, Zn, Cd, Cr, Cu ve Ni) (PTE) ve bunların ejder meyvesinde ve muzda olan biyolojik birikimlerini araştırmıştır. PTE'ler ve gübreler arasında bir korelasyon olup olmadığını görmek için farklı verimlilik testleri yapılmıştır. Topraktaki organik karbon ve azot konsantrasyonunu belirlemek için CHNS/O analiz cihazı kullanılmıştır. Ayrıca gübre girdi miktarının tespiti için organik ve inorganik fosfor miktarları analiz edilmiştir. Özellikle PTE tespiti için ICP-MS ile element analizi yapılmıştır. N, P ve K ve PTE'lerin miktarı, PTE'lerin kaynağını tespit edebilmek için karşılaştırıldı ve tartışıldı. Aşırı gübre kullanımı tespit edildi. Bu durumun olası nedenleri ve sonuçları tartışıldı. Ayrıca yapılan araştırmalar, Gazipaşa’daki sera ve açık tarla çiftliklerinde potansiyel toksik element konsantrasyonlarının toprak ve meyve örneklerinde çevre standartlarının altında olduğunu ortaya koymuştur. Örnekleme istasyonlarında organik tarım uygulamalarının inorganik tarım uygulamalarına göre daha baskın olduğu da tespit edilmiştir.