Health Effects and Legislation

Lead is ranked second on the CERCLA (Comprehensive Environmental Response, Compensation and Liability Act, 1980) Priority List of Hazardous Substances [35], indicating the national concern over lead with respect to its frequency of use, toxicity, and potential for human exposure. It is also one of the most highly regulated sub­stances in the world. As a consequence, lead has been and will continue to be studied and monitored with respect to its human and ecological toxicity. At issue, primarily, is lead’s human toxicity.

Lead can affect almost every organ and system in [the human] body. The most sensitive is the central nervous system, particularly in children. Lead also damages kidneys and the reproductive system [36].

The reader is referred to Toxicological Profile for Lead [37] for a comprehensive report on lead, including public health statement; health effects summary; chemical and physical information; production, import, use, and disposal information; descrip­tion of the potential for human exposure; analytical methods used in monitoring health effects; regulations and advisories; a valuable glossary; and a comprehensive reference list. The US Center for Disease Control and US Environmental Protection Agency also maintain extensive databases on lead.

It is not readily apparent in most general audience publications whether lead compounds are also of concern (in addition to metallic lead), and whether they are reg­ulated. An extensive review of the scientific literature, government regulations, and toxicology databases indicates, however, that within these circles, lead and lead compounds (inorganic) are grouped together and treated equally. At issue, actually, is the bioavailability of the lead, regardless of its source. Both lead and lead compounds are generally introduced into the body by either inhalation or ingestion. Inhalation is a greater concern because inhaled lead is almost entirely absorbed by the body, while only a fraction of ingested lead is absorbed [38]. The primary sink for inorganic lead is the blood. Within the body, lead is transported as if it were calcium, i. e., to soft tissues, teeth, and bones. Human exposure to inorganic lead and its compounds can result from various sources: occupational exposure, general exposure, environmental exposure (which affects general exposure), and hazardous waste disposal.

From the occupational exposure perspective, both the lead oxides used in ceramics and glasses and the lead-containing minerals from which lead is derived present risks, although appropriate precautions are generally taken to protect workers. Examples of occupational exposure warnings and carcinogen levels are presented in Table 9. In addition to these warnings about human exposure, inorganic lead and lead compounds also present a variety of dangers through chemical reactions either with other sub­stances or upon heating [37,39].

From the human health (general exposure) perspective, elemental lead and inor­ganic lead compounds are identified as possible human carcinogens by the International Agency for Research on Cancer (IARC); they are also listed in the Hazardous

Table 9 Carcinogen levels and occupational exposure warnings for lead and various lead compounds [39]

Substance

CAS No. a

Carcinogen levelb

Warnings0

Reference

Lead

7439-92-1

A3

Dust, women

ICSC 0052

PbO

1317-36-8

A3

Dust, women

ICSC 0288

PbO2

1309-60-0

A3

Women

ICSC 1001

PbsO4

1314-41-6

A3

Women

ICSC 1002

PbCO3

598-63-0

A3

All contact

ICSC 0999

PbCrO4

7758-97-6

A2

All contact, dust, women, children

ICSC 0003

a CAS: Chemical Abstracts Services

bA3: Animal carcinogen; A2: Suspected human carcinogen

c Dust, prevent dispersion of dust; women, avoid exposure of (pregnant) women; all contact, avoid all contact; children, avoid exposure of adolescents and children

Substances Data Bank provided by the National Library of Medicine. The US Environmental Protection Agency has classified lead as a Group B2 (probable) car­cinogen and as a Category I contaminant (which results in the Maximum Contaminant Level Goal (MCLG) for drinking water being set at a value of zero) [40]. In response to EPA’s classification, the State of California now regulates lead and lead compounds through Proposition 65, which requires labeling of all products that contain cancer – causing agents. The US Federal Drug Administration (FDA) also monitors lead expo­sure, because fine dust can settle on food or lead can leach from lead-containing food containers. Lead and lead compounds are regulated with respect to air quality stand­ards, drinking water standards, and blood levels. Examples of some of these standards are presented in Table 10.

From the environmental loading perspective, lead and lead compounds are regulated by EPCRA (the Emergency Planning and Community Right To Know Act, 1986) as a persistent, bioaccumulative, and toxic (PBT) chemical. As such the disposal and release of these substances are subject to Toxic Release Inventory (TRI) reporting. In 2001, the threshold reporting level for lead and lead compounds was lowered from 5,000 to 220 kg per year. Results from the 2002 TRI Report [42] indicate that in the United States over 440,000 tons of lead and lead compounds were disposed of or released into the environment. This represents more than 97% of all PBT chemical releases in that year. Lead and lead compounds are also regulated by RCRA (Resource Conservation and Recovery Act, 1976). Thus, products that contain lead or lead com­pounds must be treated as hazardous waste. Discards of lead from glass and ceramic products into the municipal solid waste stream have been increasing, primarily as the result of CRT disposal. The US EPA estimated that lead discards from TV glass increased from 10,000 tons in 1970 to over 52,000 tons in 1986; lead discards from light bulb glass increased from ~500 tons to almost 700 tons in the same period; and for other glass and ceramic applications combined, the increase was from 3,300 tons to almost 7,800 tons [43].

In the 1970s, a major concern was the documented evidence that the lead in lead – containing glazes used on whitewares used as food containers and for cooking could leach lead into food. The glass industry was responsive to these and related occupational concerns, established appropriate operating procedures and monitoring systems, as well as reduced the use of raw materials that were more soluble, such as lead carbon­ates [14,15,31,44]. Later, leaching of lead from leaded crystal, especially that used for wine decanters, became a concern [45]. This concern still exists, but is mitigated

Guideline/regulation

Organization

Limit

Units

Fate

G/R

Reference

Air content

US EPA

0.0015

mg m-3

Air

R

36

Permissible exposure

US OSHA

0.0500

mg m-3

Air

R

41

limit (TWA)

Recommended exposure

NIOSH

0.0500

mg m 3

Air

R

41

limit (TWA)

Threshold limit value (TWA)

ACGIH

0.0500

mg m 3

Air

G

39

Blood lead level of concern

US CDC

0.0100

mg dL-1

Blood

G

37

in children

Blood lead level of concern

WHO

0.0200

mg dL-1

Blood

G

37

Blood lead level of concern

ACGIH

0.0300

mg dL-1

Blood

G

37

Blood lead level of concern

US OSHA

0.0400

mg dL-1

Blood

G

37

Blood lead level – medical

US CDC

0.0450

mg dL-1

Blood

G

36

treatment in children

Blood lead level – medical

US OSHA

0.0500

mg dL-1

Blood

G

37

removal

Leaching solution

US FDA

0.0050

mg mL-1

Food

R

37

for cups and mugs

Leaching solution for pitchers

US FDA

0.0050

mg mL-1

Food

R

37

Leaching solution

US FDA

0.0300

mg mL-1

Food

R

37

for ceramicware flatware

Maximum contaminant level

US EPA

0.0500

mg L-1

Landfill R

37

Toxicity characteristic

US EPA

0.1500

mg L-1

Landfill R

37

leaching protocol limit

Drinking water action level

US EPA

0.0150

mg L-1

Water

R

37

Maximum contaminant

US EPA

0.0000

mg L-1

Water

G

37

level goals

Drinking water guidelines

WHO

0.0500

mg L-1

Water

G

37

Table 10 Representative regulatory limits and guidelines for lead (in metallic lead and various inor­

ganic lead compounds) in selected fates

G/R: G = Guideline, R = Regulation; TWA: time weighted average; US EPA: US Environmental Protection Agency; US OSHA: US Department of Occupational Safety and Health Administration; NIOSH: National Institute for Occupational Safety and Health; ACGIH: American Conference of Governmental Industrial Hygienists; US CDC: US Center for Disease Control; WHO: World Health Organization; US FDA: US Food and Drug Administration

somewhat through educational programs such as those required by Proposition 65. At present, a major concern is the proliferation of electronic waste, which includes cathode ray tubes [38]. Recent studies document concern for leaching of lead from CRTs when exposed to simulated landfill conditions, i. e., using the Toxicity Characteristic Leaching Procedure (TCLP) test protocol established by the US EPA [46].

As a consequence of these and other documented concerns over lead poisoning, various new legislative issues have come into place that will further limit the future use of lead. In the European Union, for instance, the Reduction of Hazardous Substances (RoHS) Directive has forced the removal of lead from electronics, world­wide; in the United States, the States of California, Massachusetts, Maine, and Minnesota have banned the disposal of CRTs in landfills, forcing special handling and encouraging recycling; in Japan, lead-free products have been embraced and utilized as a marketing tool. These new laws and marketing pressures, plus the plethora of existing rules and regulations, are forcing industry to consider alternative materials that do not contain lead. Examples include lead-free glasses for lamp applications [43,47], for cathode ray tubes [43,48,49], and for glazes [43,49], as well as lead-free oxides to replace PZTs and PLZTs [43,50].

2 Summary

This chapter has provided an overview of lead and lead compounds, as used in glass and ceramic products. Some of the basic physical characteristics of (metallic) lead, lead – containing minerals such as galena (PbS), and lead oxides have been provided. The lead oxide most important to glass and ceramic fabrication is litharge, PbO. Lead (oxide) is used in glasses for several reasons: to increase the refractive index of the glass, to decrease the viscosity of the glass, to increase the electrical resistivity of the glass, and to increase the X-ray absorption capability of the glass. For ceramic applications, which are primarily ferroelectric applications, the main reason to include lead (oxide) in the material is because it can significantly increase the Curie point. Leaded glasses have a wide range of chemical composition, from 2 to 77% PbO by weight, depending on the application; lead-containing ceramics typically contain 55-70 wt% Pb.

The lead oxides used in glasses and ceramics are derived from both primary lead-containing minerals and secondary recycled leaded glass. Several process steps are required to mine, concentrate, extract, smelt, and refine the lead, which is then oxidized to form lead oxide. Lead (and inorganic lead compounds such as lead oxides) is known to be toxic and probably carcinogenic to humans. As a result, these sub­stances are highly regulated and the potential for lead exposure through water, land, and air is closely monitored. The legislative burden on lead users continues to increase, which has led to significant efforts to find lead-free alternatives for both glass and ceramic products.

Acknowledgments I would like to acknowledge the research assistance of Xiaoying Zhou and Tammy Tamayo, as well as Valerie Thomas and Dele Ogunseitan for their guidance on the health risks associated with lead.