Introduction: Soil contamination by petroleum can limit plant growth and photosynthetic efficiency by reducing water and nutrient availability, altering soil physicochemical properties, and inducing direct toxicity, ultimately affecting the quality and safety of edible crops. In oil-rich regions such as Gachsaran, localized oil and petroleum product spills into agricultural soils are probable and may have significant environmental and health consequences. Given the limited information on the responses of edible herbs, this study aimed to evaluate the effects of crude oil contamination on growth, photosynthetic pigments, and selected soil parameters in two species: basil and parsley.
Materials and Methods: he experiment was conducted as a factorial arrangement in a completely randomized design with four replications in the greenhouse of the Faculty of Agriculture, Shiraz University. The first factor was species (basil and parsley), and the second factor was crude oil concentration (0, 2, 4, 6, 8, and 10 g kg⁻¹ dry soil). Oil contamination was applied using a stepwise dilution method with a volatile solvent (dichloromethane), which was completely evaporated after 72 hours of aeration under a fume hood. Measured traits included fresh and dry leaf weight, stem length, root length and volume, and photosynthetic pigment contents (chlorophyll a, chlorophyll b, and total chlorophyll). Soil physicochemical properties, including pH, electrical conductivity (EC), organic carbon, total nitrogen, and heavy metal concentrations (Fe, Pb, Zn, and Cd), were also assessed. The hydrocarbon profile in plant extracts was analyzed by GC-FID based on peak patterns.
Results: Parsley exhibited higher leaf biomass, whereas basil showed superior stem length and root parameters. Increasing crude oil concentration significantly reduced fresh and dry leaf weight, stem length, and root length and volume. At 10 g kg⁻¹, fresh leaf weight decreased by 13.2-fold and root length by 1.54-fold compared to the control, with more pronounced declines observed at 6–10 g kg⁻¹. Leaf chlorophyll content also decreased with contamination, with chlorophyll a, chlorophyll b, and total chlorophyll reduced by 1.51-, 1.84-, and 1.51-fold, respectively, at 10 g kg⁻¹. Soil pH was not significantly affected by oil contamination, whereas EC increased markedly. Organic carbon and total nitrogen declined by 1.56- and 3.10-fold at the highest contamination level compared to the control. Heavy metal accumulation in the soils also increased. Hydrocarbon peak patterns in plant extracts confirmed the uptake and translocation of certain petroleum compounds, with differences in peak intensity and profile between the two species.
Discussion and Conclusion: Crude oil contamination significantly reduced growth in both species by altering root-zone conditions, which included increased EC, decreased organic carbon and nitrogen, and elevated heavy metals, and by limiting photosynthesis through reduced chlorophyll content, with the most severe effects being observed at higher contamination levels such as 6–10 g kg⁻¹. These findings suggest that basil and parsley can effectively serve as bioindicator species for monitoring the early effects of petroleum contamination under controlled conditions. The identified growth reduction thresholds provide a basis for risk assessment and management of contaminated soils. However, due to the greenhouse setting, field studies on naturally contaminated soils are recommended to enhance the generalizability of the results.