Soil Lead Concentration and Speciation in Community Farms of Newark, New Jersey, USA

Abstract

Farmed urban soils often bear legacies of historic contamination from anthropogenic and industrial sources. Soils from seven community farms in Newark, New Jersey (NJ), USA, were analyzed to determine the concentration and speciation of lead (Pb) depending on garden location and cultivation status. Samples were evaluated using single-step 1 M nitric acid (HNO3) and Tessier sequential extractions in combination with X-ray absorption fine structure spectroscopy (XAFS) analysis. Single-step extractable Pb concentration ranged from 22 to 830 mg kg−1, with 21% of samples reporting concentrations of Pb > 400 mg kg−1, which is the NJ Department of Environmental Protection (NJDEP) limit for residential soils. Sequential extractions indicated lowest Pb concentrations in the exchangeable fraction (0–211 mg kg−1), with highest concentrations (0–3002 mg kg−1) in the oxidizable and reducible fractions. For samples with Pb > 400 mg kg−1, Pb distribution was mostly uniform in particle size fractions of <0.125–1 mm, with slightly higher Pb concentrations in the <0.125 mm fraction. XAFS analysis confirmed that Pb was predominantly associated with pyromorphite, iron–manganese oxides and organic matter. Overall results showed that lowest concentrations of Pb are detected in raised beds, whereas uncultivated native soil and parking lot samples had highest values of Pb. As most of the Pb is associated with reducible and oxidizable soil fractions, there is a lower risk of mobility and bioavailability. However, Pb exposure through ingestion and inhalation pathways is still of concern when directly handling the soil. With increasing interest in urban farming in cities across the USA, this study highlights the need for awareness of soil contaminants and the utility of coupled macroscopic and molecular-scale geochemical techniques to understand the distribution and speciation of soil Pb.

Trace Metal Contamination in Community Garden Soils across the United States

“…Cadmium, along with lead and arsenic, is among the top 10 hazardous substances in terms of public health and is also one of the most detected metals in community garden soils [4,8,13]. The health effects of cadmium include renal dysfunction, bone damage, coughing, emphysema, headache, hypertension, lung and prostate cancer, lymphocytosis, microcytic hypochromic anemia, testicular atrophy, and vomiting [26,37].…”

“…Lead is a known neurotoxin that can negatively affect a child's neurological development, overall growth, and even academic achievement [13,22]. Approximately 412,000 avoidable deaths can be linked back to lead contamination [47].…”

“…Many of these contaminated sites in urban areas are a result of past industrialization. Cities also have many potential sources of trace metal contamination, such as old chipping lead paint, gasoline, runoff from nearby roads, fertilizer, municipal solid waste disposal, nearby mining, and nearby smelting [11][12][13][14][15]. The lack of consideration towards soil quality could lead to community members ingesting unhealthy levels of trace metals through inhalation or ingestion [16].…”

“…In this paper, we selected and reviewed published manuscripts in the United States concerning trace metal and metalloid contamination (Pb, As, Cd, and Zn) in urban community gardens. Studies on trace metal contamination in community gardens have mainly focused on quantifying lead contamination, mapping contamination in the region, assessing the relationship with land uses and local contaminant sources, analyzing variations in geographical regions, comparing concentrations to the available public health guidelines, measuring the speciation and mobility of metals and metalloids, and examining the influence of garden characteristics such as raised beds [1,11,[13][14][15]17,[20][21][22][23][24][25]. This paper presents the plant uptake of trace metals, various exposure pathways to trace metals in community gardens, environmental justice issues, the effect of soil pH and plant nutrients on trace metals, and various soil remediation applications.…”